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Document And Entity Information - USD ($) $ in Millions	12 Months Ended
Document And Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Mar. 09, 2018	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	PROTEON THERAPEUTICS INC
Entity Central Index Key	0001359931
Trading Symbol	prto
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Common Stock, Shares Outstanding (in shares)		17,674,729
Entity Public Float			$ 16.3
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 21,170	$ 36,392
Available-for-sale investments	20,971	4,925
Prepaid expenses and other current assets	1,339	1,438
Total current assets	43,480	42,755
Property and equipment, net	259	372
Other non-current assets	240	393
Total assets	43,979	43,520
Current liabilities:
Accounts payable	291	556
Accrued expenses	8,949	4,523
Total current liabilities	9,240	5,079
Total liabilities	9,240	5,079
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred Stock	0	0
Common stock, $0.001 par value, 100,000,000 shares authorized at December 31, 2017 and 2016; 17,674,729 and 16,603,559 shares issued and outstanding at December 31, 2017 and 2016, respectively	18	17
Additional paid-in capital	202,953	198,201
Accumulated deficit	(189,741)	(159,777)
Accumulated other comprehensive loss	(14)
Total stockholders’ equity	34,739	38,441
Total liabilities and stockholders’ equity	43,979	43,520
Series A Convertible Preferred Stock [Member]
Stockholders’ equity:
Preferred Stock	$ 21,523

Consolidated Balance Sheets (Parentheticals) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	17,674,729	16,603,559
Common stock, shares oustanding (in shares)	17,674,729	16,603,559
Series A Convertible Preferred Stock [Member]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	22,000	0
Preferred stock, shares issued (in shares)	22,000	0
Preferred stock, shares outstanding (in shares)	22,000	0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 21,686	$ 18,869	$ 12,381
General and administrative	8,676	9,836	8,489
Total operating expenses	30,362	28,705	20,870
Loss from operations	(30,362)	(28,705)	(20,870)
Other income (expense):
Investment income	259	193	144
Other income (expense), net	139	(14)	(651)
Total other income (expense)	398	179	(507)
Net loss	(29,964)	(28,526)	(21,377)
Foreign currency translation adjustment	6	0
Unrealized (loss) gain on available-for-sale investments	(20)	11	(5)
Comprehensive loss	(29,978)	(28,515)	(21,382)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	29,964	28,526	21,377
Accretion of convertible preferred stock to redemption value	(6,747)
Net loss attributable to common stockholders	$ (36,711)	$ (28,526)	$ (21,377)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (2.13)	$ (1.72)	$ (1.30)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	17,274,326	16,561,799	16,464,123
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 3,227	$ 3,343	$ 2,164
Included in other expense, above, are the following amounts from forward foreign currency contracts:
Realized losses from forward foreign currency contracts		(61)	(52)
Unrealized gains (losses) from forward foreign currency contracts		127	(537)
Total		66	(589)
Research and Development Expense [Member]
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	1,109	1,114	650
General and Administrative Expense [Member]
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 2,118	$ 2,229	$ 1,514

Statements of Stockholders' Equity - USD ($) $ in Thousands	Series A Preferred Stock [Member] Preferred Stock [Member]	Series A Preferred Stock [Member] Additional Paid-in Capital [Member]	Series A Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2014				16,448,455
Balance at Dec. 31, 2014				$ 16	$ 192,324	$ (109,874)	$ (6)	$ 82,460
Exercise of common stock options (in shares)				45,413
Exercise of common stock options					88			88
Issuance of common stock upon ESPP purchase (in shares)				7,632
Issuance of common stock upon ESPP purchase					75			75
Stock-based compensation expense					2,164			2,164
Unrealized (loss) gain on available-for-sale investments							(5)	(5)
Net loss						(21,377)		(21,377)
Balance (in shares) at Dec. 31, 2015				16,501,500
Balance at Dec. 31, 2015				$ 16	194,651	(131,251)	(11)	63,405
Exercise of common stock options (in shares)				97,521
Exercise of common stock options				$ 1	196			197
Issuance of common stock upon ESPP purchase (in shares)				4,538
Issuance of common stock upon ESPP purchase					11			11
Stock-based compensation expense					3,343			3,343
Unrealized (loss) gain on available-for-sale investments							11	11
Net loss						(28,526)		(28,526)
Balance (in shares) at Dec. 31, 2016				16,603,559
Balance at Dec. 31, 2016				$ 17	198,201	(159,777)		$ 38,441
Exercise of common stock options (in shares)				74,001				74,001
Exercise of common stock options					108			$ 108
Issuance of common stock upon ESPP purchase (in shares)				100,358
Issuance of common stock upon ESPP purchase					130			130
Stock-based compensation expense					3,227			3,227
Unrealized (loss) gain on available-for-sale investments								(20)
Net loss						(29,964)		(29,964)
Issuance of stock, net of issuance costs (in shares)	22,000			896,811
Issuance of stock, net of issuance costs	$ 14,776	$ 6,747	$ 21,523	$ 1	1,287			1,288
Accretion of Series A Convertible Preferred Stock	$ 6,747				(6,747)
Other comprehensive loss							(14)	(14)
Balance (in shares) at Dec. 31, 2017	22,000			17,674,729
Balance at Dec. 31, 2017	$ 21,523			$ 18	$ 202,953	$ (189,741)	$ (14)	$ 34,739

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (29,964)	$ (28,526)	$ (21,377)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	148	123	57
Amortization of premium/discount on available-for-sale securities	(2)	131	651
Unrealized (gain) loss on forward foreign currency contracts included in net income		(127)	537
Foreign currency remeasurement (gain)/loss	(173)	76	75
Stock-based compensation	3,227	3,343	2,164
Changes in:
Prepaid expenses and other assets	297	246	(899)
Interest receivable	(46)	(26)	(32)
Accounts payable and accrued expenses	4,161	1,073	1,258
Net cash used in operating activities	(22,352)	(23,687)	(17,566)
Investing activities
Purchases of available-for-sale investments	(32,942)	(39,756)	(88,644)
Proceeds from maturities of available-for-sale investments	16,878	59,943	75,505
Proceeds from sale of available-for-sale investments			2,006
Purchase of property and equipment	(35)	(271)	(198)
Net cash (used in) provided by investing activities	(16,099)	19,916	(11,331)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	1,288
Proceeds from the issuance of Series A Convertible Preferred Stock, net of issuance costs	21,523
Proceeds from issuance of common stock under ESPP	130	11	75
Exercise of stock options	108	197	88
Net cash provided by financing activities	23,049	208	163
Effect of exchange rate changes on cash	180	(76)	(75)
Decrease in cash and cash equivalents	(15,222)	(3,639)	(28,809)
Cash and cash equivalents, beginning of period	36,392	40,031	68,840
Cash and cash equivalents, end of period	21,170	36,392	40,031
Supplemental disclosure of non-cash investing and financing activities
Accretion of convertible preferred stock	$ 6,747

Note 1 - Organization and Operations

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Nature of Operations [Text Block]

Organization and Operations

The Company

Proteon Therapeutics, Inc. (the “Company”) is a late-stage biopharmaceutical company focused on the development of novel,

first

-in-class pharmaceuticals to address the medical needs of patients with kidney and vascular disease. The Company was formed in

June 2001

and incorporated on

March 24, 2006.

The Company devotes substantially all of its efforts to product research and development, initial market development and raising capital. The Company has

not

generated any product revenue related to its primary business purpose to date and is subject to a number of risks similar to those of other development stage companies, including dependence on key individuals, competition from other companies, the need for development of commercially viable products and the need to obtain adequate additional financing to fund the development of its product candidates. The Company is also subject to a number of risks similar to other companies in the biotechnology industry, including regulatory approval of products, uncertainty of market acceptance of products, competition from therapeutic alternatives and larger companies, compliance with government regulations, protection of proprietary technology, dependence on

third

parties and product liability.

As of

December 31, 2017,

the Company had cash, cash equivalents and available-for-sale investments of

$42.1

million. The Company believes that its existing cash, cash equivalents and available-for-sale investments will be sufficient to fund operations and capital expenditures into the

fourth

quarter of

2019.

The Company had an accumulated deficit of

$189.7

million as of

December 31, 2017.

Note 2 - Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Significant Accounting Policies [Text Block]

Summary of Significant Accounting Policies

At-The-Market Equity Offering Program

November 12, 2015,

the Company filed a shelf registration statement on Form S-

(the “Registration Statement”), and entered into a Sales Agreement with Cowen and Company, LLC (the “Sales Agreement”) to establish an at-the-market (“ATM”) equity offering program pursuant to which they are able, with the Company’s authorization, to offer and sell up to

$40

million of the Company’s Common Stock at prevailing market prices from time to time. The Registration Statement became effective on

January 12, 2016.

The Company pays Cowen a commission equal to

of the gross proceeds of the sales price of all shares sold through it as sales agent under the Sales Agreement. The offering costs are offset against proceeds from the sale of common stock under this agreement. The Company filed a prospectus supplement on

March 16, 2017

because the Company is currently subject to General Instruction

I.B.6

of Form S-

which limits the amounts that the Company

may

sell under the Registration Statement. For the year ended

December 31, 2017,

the Company sold

896,811

shares of Common Stock under the Sales Agreement for aggregate gross proceeds of

$1.4

million, respectively. For the year ending

December 31, 2017,

total offering costs of

$0.1

million were offset against the proceeds from the sale of common stock.

Series A Preferred Financing

June 22, 2017,

the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with a syndicate of current and new institutional investors, led by an affiliate of Deerfield Management Company, L.P., pursuant to which the Company agreed to issue and sell to the investors an aggregate of

22,000

shares of the Company’s Series A Convertible Preferred Stock, par value

$0.001

per share (the “Transaction”), for a purchase price of

$1,000

per share, or an aggregate gross purchase price of

$22.0

million, all upon the terms and conditions set forth in the Purchase Agreement. The Company closed this Transaction on

August 2, 2017 (

see Note

August 2, 2017,

the Company entered into a registration rights agreement with the Investors (the “Registration Rights Agreement”). On

August 3, 2017,

in accordance with the Registration Rights Agreement, the Company filed a registration statement on Form S-

to register the common stock issuable upon conversion of the Preferred Shares. The registration statement became effective on

August 21, 2017.

Basis of Presentation, Principles of Consolidation and Use of Estimates

The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are

not

limited to, estimates related to stock-based compensation expense, clinical trial accruals and reported amounts of expenses during the reported period. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results

may

differ from those estimates or assumptions.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company's chief operating decision maker view the Company's operations and manage its business in

one

operating segment, which is the business of developing and commercializing vonapanitase for the treatment of renal and vascular disease. Currently, the Company operates in only

one

geographic segment.

Fair Value of Financial Instruments

The Company’s financial instruments consist of cash and cash equivalents, available-for-sale investments, forward foreign currency contracts (see Note

), accounts payable, and accrued liabilities. The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic

820,

Fair Value Measurement and Disclosures

, established a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the financial instrument based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the financial instrument and are developed based on the best information available under the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported or disclosed fair value of the financial instruments and is

not

a measure of the investment credit quality. Fair value measurements are classified and disclosed in

one

of the following

three

categories:

Level

1—Valuations

based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level

2—Valuations

based on quoted prices for similar assets or liabilities in markets that are

not

active or for which all significant inputs are observable, either directly or indirectly.

Level

3—Valuations

that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level

A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Financial instruments measured at fair value on a recurring basis include cash equivalents, available-for-sale investments and forward foreign currency contracts (see Note

). There have been

changes to the valuation methods utilized by the Company during the years ended

December 31, 2017

and

2016.

The Company evaluates transfers between levels at the end of each reporting period. There were

transfers of financial instruments between levels during the years ended

December 31, 2017

and

2016.

Derivative Financial Instruments

The Company enters into forward foreign currency contracts to mitigate its exposure to fluctuations in the exchange rates between the Swiss Franc and the U.S. dollar (see Note

). The Company records these derivative financial instruments on the consolidated balance sheets at fair value. Although these derivative contracts are intended to economically hedge foreign exchange risk, the Company has

not

elected to apply hedge accounting. As such, changes in the fair value of these instruments are recorded directly in earnings as a component of other income (expense), as they occur. The Company executes its derivative instruments with financial institutions that the Company judges to be credit-worthy, defined as institutions that hold an investment-grade credit rating.

Recent Accounting Pronouncements

May 2014,

the FASB issued ASU

2014

09,

“Revenue from Contracts with Customers”

(“ASU

2014

09”

), a new standard on revenue recognition providing a single, comprehensive revenue recognition model for all contracts with customers. The new revenue standard is based on the principle that revenue should be recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The new standard is effective beginning

January 1, 2018,

with

early adoption permitted. Earlier application is permitted only as of annual reporting periods beginning after

December 15, 2016,

including interim reporting periods within that reporting period. The amendments

may

be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of initial application. The Company does

not

expect this guidance to have a material impact on its condensed consolidated financial statements, if any.

February 2016,

the FASB issued ASU

2016

02,

Leases (Topic

842

): Amendments to FASB Codification

(“ASU

2016

02”

), which increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and disclosing key information about leasing arrangements. At the lease commencement date, the lessee must recognize a lease liability and right-of-use asset, which is initially measured at the present value of future lease payments. ASU

2016

is effective for public companies for fiscal years, and interim periods within those fiscal years, beginning after

December 15, 2018,

with early adoption permitted. ASU

2016

must be adopted using a modified retrospective transition, and provides for certain practical expedients. Transition will require application of the new guidance at the beginning of the earliest comparative period presented. The Company is currently evaluating the impact of the new guidance on its consolidated financial statements.

March 2016,

the FASB issued ASU

2016

09,

Compensation - Stock Compensation (Topic

718

): Improvements to Employee Share-Based Payment Accounting

(“ASU

2016

09”

), which simplifies various aspects of the accounting for share-based payments, including accounting for income taxes, earnings per share, and forfeitures. ASU

2016

is effective for annual periods beginning after

December 15, 2016,

and interim periods within those annual periods with early adoption permitted. The Company adopted ASU

2016

during the quarter ended

March 31, 2017.

As a result of adoption, the deferred tax assets associated with net operating losses increased by

$0.6

million. These amounts were offset by a corresponding increase in the valuation allowance. In addition, the Company has elected to recognize the effect of forfeitures in compensation cost when they occur rather than estimate forfeitures in advance. The Company will reverse any previously recognized compensation cost for an award in the period that the award is forfeited. The adoption had an immaterial impact on the condensed consolidated financial statements.

August 2016,

the FASB issued ASU

2016

15,

Statement of Cash Flows (Topic

230

): Classification of Certain Cash Receipts and Cash Payments

(“ASU

2016

15”

), which provides clarification regarding how certain cash receipts and cash payment are presented and classified in the statement of cash flows. This update addresses

eight

specific cash flow issues with the objective of reducing the existing diversity in practice. This update is effective for annual and interim periods beginning after

December 15, 2017,

which will require the Company to adopt these provisions in the

first

quarter of fiscal

2019

using a retrospective approach. Early adoption is permitted. The Company does

not

expect the adoption of this guidance to have a material impact on its consolidated financial statements.

May 2017,

the FASB issued ASU

No.

2017

09,

Compensation - Stock Compensation (Topic

718

): Scope of Modification Accounting

(“ASU

2017

09”

), which clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. The new guidance will reduce diversity in practice and result in fewer changes to the terms of an award being accounted for as modifications. Under ASU

2017

09,

an entity will

not

apply modification accounting to a share-based payment award if the award’s fair value, vesting conditions and classification as an equity or liability instrument are the same immediately before and after the change. ASU

2017

will be applied prospectively to awards modified on or after the adoption date. The guidance is effective for annual periods, and interim periods within those annual periods, beginning after

December 15, 2017.

Early adoption is permitted. The Company is evaluating the impact of the adoption of this guidance on its financial statements but does

not

expect it to have a material impact.

Cash and Cash Equivalents

The Company considers all highly liquid investments with maturities of

days or less from the purchase date to be cash equivalents. Cash and cash equivalents are held in depository and money market accounts and are reported at fair value.

Short-Term Investments

The Company classifies its investments as available-for-sale and records such assets at estimated fair value in the consolidated balance sheets, with unrealized gains and losses, if any, reported as a component of other comprehensive income (loss) within the consolidated statements of operations and comprehensive loss and as a separate component of stockholders' equity (deficit). The Company invests its excess cash balances primarily in government debt securities and money market funds with strong credit ratings and maturities of less than

one

year. There have been

realized gains and losses for the years ended

December 31, 2017,

2016

and

2015.

At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security's relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. When the Company determines that a decline in the fair value below its cost basis is other-than-temporary, the Company recognizes an impairment loss in the year in which the other-than-temporary decline occurred. There have been

other-than-temporary declines in value of short-term investments for the years ended

December 31, 2017,

2016

and

2015,

as it is more likely than

not

the Company will hold the securities until maturity or a recovery of the cost basis.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash, cash equivalents and short-term investments. The Company's cash and cash equivalents are held in accounts with financial institutions that management believes are creditworthy. The Company's investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentration of credit risk. These amounts at times

may

exceed federally insured limits. The Company has

not

experienced any credit losses in such accounts and does

not

believe it is exposed to any significant credit risk on these funds. The Company has

financial instruments with off-balance sheet risk of loss.

Property and Equipment

Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do

not

improve or extend the lives of the respective assets are expensed to operations as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the results of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows:

Asset	Estimated Useful Life (in years)
Computer equipment and software	3
Furniture, fixtures and other	5
Laboratory equipment	7

Research and Development Costs

Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, facilities and overhead, clinical study and related clinical manufacturing costs, regulatory and other related costs. Nonrefundable advanced payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.

Stock-Based Compensation Expense

The Company accounts for its stock-based compensation awards to employees and directors in accordance with FASB ASC Topic

718,

Compensation-Stock Compensation

(“ASC

718”

). ASC

718

requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the consolidated statements of operations and comprehensive loss based on their grant date fair values. Compensation expense related to awards to employees is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Share-based payments issued to non-employees are recorded at their fair values and are periodically revalued as the equity instruments vest and are recognized as expense over the related service period in accordance with the provisions of ASC

718

and FASB ASC Topic

505,

Equity

and are expensed using an accelerated attribution model.

The Company estimates the fair value of its stock options using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including (a) the expected stock price volatility, (b) the expected term of the award, (c) the risk-free interest rate, (d) expected dividends and (e) the estimated fair value of its Common Stock on the measurement date. Due to the lack of company specific historical and implied volatility data of its Common Stock, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry and with historical share price information sufficient to meet the expected term of the stock based awards. The Company computes historical volatility data using the daily closing prices for the selected companies' shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Due to the lack of Company specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. The expected term for non-employee awards is the remaining contractual term of the option. The risk-free interest rates are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid and does

not

expect to pay dividends in the foreseeable future. Refer to Note

“

Use of Estimates

,” for a discussion of the Company's estimated fair value of its Common Stock.

Income Taxes

Income taxes are recorded in accordance with FASB ASC Topic

740,

“Income Taxes” (“ASC

740”

), which provides for deferred taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial reporting and tax reporting basis of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. Valuation allowances are provided if based upon the weight of available evidence, it is more likely than

not

that some or all of the deferred tax assets will

not

be realized. The Company has evaluated available evidence and concluded that the Company

may

not

realize the benefit of its deferred tax assets; therefore, a valuation allowance has been established for the full amount of the deferred tax assets.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC

740.

When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than

not

be realized. The determination as to whether the tax benefit will more likely than

not

be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of

December 31, 2017

and

2016,

the Company did

not

have any significant uncertain tax positions. The Company's practice is to recognize interest and/or penalties related to income tax matters in income tax expense. See Note

for further details.

Net Income (Loss) per Share Attributable to Common Stockholders

Basic net income (loss) per share is calculated by dividing net income (loss) attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options and warrants using the treasury stock method.

The Company follows the

two

-class method when computing net income (loss) per share in periods when issued shares that meet the definition of participating securities are outstanding. The

two

-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The

two

-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders when participating securities are outstanding, losses are

not

allocated to the participating securities. For purposes of calculating diluted net income per share attributable to common shareholders, preferred stock, stock options, warrants and convertible debt are considered common stock equivalents.

Comprehensive Loss

Comprehensive loss consists of net income or loss and changes in equity during a period from transactions and other events and circumstances generated from non-owner sources. The Company's net loss equals comprehensive loss, net of any changes in the unrealized gains and losses of the Company's short-term investments, held as available-for-sale, and foreign currency translation for all periods presented.

Subsequent Events

The Company considers events or transactions that occur after the balance sheet date but prior to the date the consolidated financial statements are available to be issued for potential recognition or disclosure in the financial statements. The Company has completed an evaluation of all subsequent events after the consolidated balance sheet date of

December 31, 2017

to ensure that this filing includes appropriate disclosure of events both recognized in the consolidated financial statements as of

December 31, 2017

and events which occurred subsequently but were

not

recognized in the consolidated financial statements.

Note 3 - Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Fair Value Disclosures [Text Block]

Below is a summary of assets and liabilities measured at fair value (in thousands):

	As of December 31, 2017
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	11,662	$	-	$	-	$	11,662
Government securities		20,971		-		-		20,971
Total	$	32,633	$	-	$	-	$	32,633

	As of December 31, 2016
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	28,876	$	-	$	-	$	28,876
Government securities		4,925		-		-		4,925
Total	$	33,801	$	-	$	-	$	33,801

As of

December 31, 2017,

and

2016,

the Company’s cash equivalents consist principally of money market funds and government debt securities with original maturities of

days or less. Government securities consist principally of government debt securities and money market funds which are classified as available-for-sale.

Available-for-sale securities at

December 31, 2017

and

2016

consist of the following (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2017
Government securities
(Due within 1 year)	$	20,991	$	-	$	(20	)	$	20,971
	$	20,991	$	-	$	(20	)	$	20,971

December 31, 2016
Government securities
(Due within 1 year)	$	4,924	$	1	$	-		$	4,925
	$	4,924	$	1	$	-		$	4,925

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Note 4 - Derivative Financial Instruments

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Derivative Instruments and Hedging Activities Disclosure [Text Block]

4.	Derivative Financial Instruments

Beginning in

May 2015

and through

2016,

the Company purchased Swiss Francs and entered into a series of forward foreign currency contracts to mitigate its exposure to fluctuations in the U.S. dollar value of forecasted transactions denominated in Swiss Franc. The latter are considered derivative financial instruments that the Company records on the consolidated balance sheet at fair value. The Company elected

not

to apply hedge accounting to these instruments. As a result, during the year ended

December 31, 2016,

the Company experienced unrealized gains within other income (expense), net, in the consolidated statements of operations from the mark-to-market of outstanding forward foreign currency contracts. As of

December 31, 2016,

all forward foreign currency contracts had been settled and are

longer outstanding.

Note 5 - Property and Equipment, Net

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Property, Plant and Equipment Disclosure [Text Block]

Property and Equipment, net

Property and equipment, net consists of the following (in thousands):

	As of December 31,
	2017			2016

Computer equipment and software	$	192		$	141
Furniture, fixtures, and other		302			318
Laboratory equipment		477			478
		971			937
Accumulated depreciation		(712	)		(565	)
Property and equipment, net	$	259		$	372

Depreciation expense for the years ended

December 31, 2017,

2016

and

2015

was

$0.1

million,

$0.1

million, and

$0.1

million, respectively.

Note 6 - Accrued Expenses

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Accounts Payable and Accrued Liabilities Disclosure [Text Block]

Accrued Expenses

Accrued expenses consist of the following (in thousands):

	As of December 31,
	2017		2016

Payroll and employee-related costs	$	1,318	$	1,139
Contracted service costs		7,218		2,891
Professional fees and other		413		493
Total	$	8,949	$	4,523

Note 7 - Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Commitments and Contingencies Disclosure [Text Block]

Commitments and Contingencies

Significant Contracts and Agreements

February 2002,

the Company entered into an agreement to license certain intellectual property with Johns Hopkins University. The agreement calls for payments to be made by the Company upon the commencement of product sales, in the form of a royalty of

2.5%

on net sales of the product. As of

December 31, 2017

the Company has

not

commenced product sales and therefore has recognized

royalties on product sales.

July 2015,

the Company entered into a manufacturing services agreement with Lonza Ltd, or (“Lonza”) for the processing, development and manufacturing of the active pharmaceutical ingredient (“API”) in its lead product candidate, vonapanitase. Under the agreement, the Company will issue purchase orders authorizing Lonza to manufacture API batches and will pay for the services and batches in accordance with terms and assumptions in the agreement and to be set forth in a project plan. As of

December 31, 2017,

the Company has issued a purchase order for

7.6

million Swiss Francs, approximately

$7.8

million at current exchange rates, for the manufacturing of

three

batches that commenced in

July 2017

and

one

batch to commence by the end of

2019.

As of

December 31, 2017,

nearly all of the services related to the

three

batches that commenced in

July 2017

have been rendered under this purchase order.

Operating Leases

The Company has various non-cancellable operating leases for facilities and office equipment that expire at various dates through

2019.

August 2017,

the Company entered into an Amendment (the “Lease Amendment”) to the existing Lease Agreement dated

July 13, 2009 (

the “Lease Agreement”), with Boston Properties Limited Partnership (“Lessor”) pursuant to which the Company has agreed to (i) extend the term of the lease for a period of

fifteen

(

) months from

June 30, 2018

until

September 30, 2019

and (ii) increase the Company’s office space under the Lease Agreement by

2,552

square feet of additional property for a total of approximately

7,500

square feet of property (the “Leased Property”). The Leased Property is located at

200

West St., Waltham, Massachusetts. In addition, the Company has the option to extend the term of the Lease Agreement for an additional

one

-year period upon the Company’s written notice to the Lessor at least

six

months prior to the expiration of the term. Rental expense for each of the years ended

December 31, 2017,

2016

and

2015

was

$0.2

million.

Future minimum payments required under operating leases as of

December 31, 2017

are summarized as follows (in thousands):

Year Ending December 31:	Amount

2018	$	270
2019		207
Total minimum lease payments	$	477

In addition to the base rent, the Company is also responsible for its share of operating expenses and real estate taxes, in accordance with the terms of the lease agreement. As of

December 31, 2017,

the Company has provided a security deposit in the amount of

$22,000

to the lessor.

Restricted cash related to facilities leases

December 31, 2017

and

2016,

the Company had

$22,000

and

$14,000,

respectively, in an outstanding letter of credit to be used as collateral for leased premises. At

December 31, 2017

and

2016,

the Company pledged an aggregate of

$22,000

and

$14,000,

respectively, to the bank as collateral for the letter of credit, which is included in other non-current assets.

Note 8 - Series A Preferred Financing

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Preferred Stock [Text Block]

8.	Series A Preferred Financing

August 2, 2017,

the Company issued and sold

22,000

shares of the Company’s Series A Convertible Preferred Stock, par value of

$0.001

per share (the “Series A Preferred”), for a purchase price of

$1,000

per share, or aggregate purchase price and gross proceeds of

$22.0

million, all upon the terms and conditions set forth in the Securities Purchase Agreement dated as of

June 22, 2017.

The Company incurred

$0.5

million of issuance costs in connection with the transaction. Each share of Series A Preferred is convertible into approximately

1,005

shares of the Company’s Common Stock at a conversion price of

$0.9949

per share, in each case subject to adjustment for any stock splits, stock dividends and similar events, provided that any conversion of Series A Preferred by a holder into shares of Common Stock is prohibited if, as a result of such conversion, the holder, together with its affiliates and any other person or entity whose beneficial ownership of the Company’s Common Stock would be aggregated with such holder’s for purposes of Section

(d) of the Exchange Act would beneficially own more than

9.985%

of the total number of shares of Common Stock issued and outstanding after giving effect to such conversion.

Upon issuance, each share of Series A Preferred included an embedded beneficial conversion feature as the market price of the Company’s Common Stock on the date of issuance of the Series A Preferred was

$1.30

per share. As a result, the Company recorded the intrinsic value of the beneficial conversion feature of

$6.7

million as a discount on the Series A Preferred at issuance. As the Series A Preferred is immediately convertible upon issuance and does

not

include a stated redemption date, the discount on the Series A Preferred was immediately accreted.

The Company evaluated the Series A Preferred for liability or equity classification in accordance with the provisions of ASC

480,

Distinguishing Liabilities from Equity, and determined that equity treatment was appropriate because the Series A Preferred did

not

meet the definition of the liability instruments defined thereunder for convertible instruments. Specifically, the Series A Preferred are

not

mandatorily redeemable and do

not

embody an obligation to buy back the shares outside of the Company’s control in a manner that could require the transfer of assets. Additionally, the Company determined that the Series A Preferred would be recorded as permanent equity,

not

temporary equity, based on the guidance of ASC

480

given that there is

scenario where the holders of equally and more subordinated equity of the entity would

not

be entitled to also receive the same form of consideration upon the occurrence of the event that gives rise to the redemption.

Dividends

Holders of the Series A Preferred Stock are entitled to receive dividends, if and when declared by the Board of Directors.

Liquidation Preference

Holders of the Series A Preferred Stock have preference in the event of a liquidation or dissolution of the Company equal to

$0.001

per share, plus any declared dividends.

Thereafter, the Holders of the shares of Series A Preferred Stock shall share ratably in any distributions and payments of any remaining assets of the Company, on an as converted basis, with the holders of Common Stock.

Voting Rights

Except for matters with specific voting rights as provided in the Series A Preferred Stock Purchase Agreement, the Holders of shares of Series A Preferred Stock have

voting rights.

Note 9 - Common Stock

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Common Stock [Text Block]

Common Stock

General

December 31, 2017,

the Company has

100,000,000

shares of Common Stock authorized for issuance,

$0.001

par value per share, of which

17,674,729

shares were issued and outstanding.

Reserved for Future Issuance

The Company has the following shares of Common Stock reserved for future issuance:

	December 31,		December 31,
	2017		2016

Conversion of Series A Preferred Stock		22,112,775		-
Stock-based compensation awards		3,572,457		2,982,470
Employee Stock Purchase Plan		192,463		292,821
Total		25,877,695		3,275,291

Note 10 - Stock-based Compensation

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

10.

Stock-based Compensation

August 21, 2014,

the Company’s Board of Directors adopted the

2014

Equity Incentive Plan (the

“2014

Plan”), the

2014

Employee Stock Purchase Plan (the

“2014

ESPP”) and the

2006

Equity Incentive Plan (the

“2006

Plan”). On

October 3, 2014,

the stockholders approved these plans. The stockholders also approved an amendment to the

2014

Plan on

July 31, 2017.

The Plans provide for the grant of incentive and non-statutory stock options, stock appreciation rights, restricted stock and stock unit awards, performance units, stock grants and qualified performance-based awards. Under the

2006

Plan,

new stock compensation awards will be granted subsequent to the completion of the Company’s IPO. The Company initially reserved

704,000

shares of Common Stock for issuance under the

2014

Plan. The

2014

Plan provides that the number of shares reserved and available for issuance under the

2014

Plan will automatically increase each

January 1,

beginning

January 1, 2015

four

percent of the outstanding shares of Common Stock on the immediately preceding

December 31

or such lesser number of shares as determined by the Company’s Board of Directors prior to each such

January

1st.

Terms of the stock awards, including vesting requirements, are determined by the Board of Directors, subject to the provisions of the Plans. Options granted by the Company typically vest over

three

four

years. Certain awards provide for accelerated vesting if there is a change in control as defined in the Plans. Stock options outstanding under the

2006

Plan are exercisable from the date of grant for a period of

ten

years. Stock options granted under the

2014

Plan are exercisable only upon vesting. For options granted to date, the exercise price equaled the fair value of the Common Stock as determined by the Board of Directors on the date of grant.

Stock-based compensation expense

Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s consolidated statements of operations as follows (in thousands):

	Year Ended December 31,
	2017		2016		2015

Research and development	$	1,109	$	1,114	$	650
General and administrative		2,118		2,229		1,514
Total	$	3,227	$	3,343	$	2,164

The Company estimates the fair value of each employee stock award on the grant date using the Black-Scholes option-pricing model based on the following assumptions regarding the fair value of the underlying Common Stock on each measurement date:

	Year Ended December 31,
	2017			2016			2015
Weighted average expected volatility		94.5	%		84.4	%		79.8	%
Expected term (in years)		6.06			6.05			6.11
Risk free interest rate		2.09	%		1.45	%		1.76	%
Expected dividend yield		0	%		0	%		0	%

Stock options issued to non-employees are accounted for using the fair value method of accounting; they are periodically revalued as the options vest and are recognized as expense over the related service period. The total expense related to all options granted to non-employees for the years ended

December 31, 2017,

2016

and

2015

was

$0,

and

$2,000,

respectively.

Stock Options

The following table summarizes stock option activity for employees and non-employees:

	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value

Outstanding at December 31, 2016		2,166,254		$	8.55		7.1	$	124
Granted		719,337		$	1.99
Exercised		(74,001	)	$	1.45
Forfeited		(30,272	)	$	10.69
Expired		(100,246	)	$	2.60
Outstanding at December 31, 2017		2,681,072		$	7.18		6.8	$	121
Exercisable at December 31, 2017		1,495,789		$	8.18		5.9	$	85
Vested or expected to vest at December 31, 2017 (1)		2,681,072		$	7.18		6.8	$	121

____________________

(

) Represents the number of vested options at

December 31, 2017

plus the number of unvested options expected to vest based on the unvested options outstanding at

December 31, 2017.

During the year ended

December 31, 2017,

the Company granted stock options to purchase an aggregate of

719,337

shares of its Common Stock with a weighted-average grant date fair value of

$1.99.

During the year ended

December 31, 2016,

the Company granted stock options to purchase an aggregate of

132,495

shares of its Common Stock with a weighted-average exercise price of

$7.11

and a weighted-average grant date fair value of

$5.08.

During the year ended

December 31, 2015,

the Company granted stock options to purchase an aggregate of

1,010,256

shares of its Common Stock with a weighted-average grant date fair value of

$9.34

The total intrinsic value of options exercised in the years ended

December 31, 2017

and

2016

was

$27,000

and

$0.6

million, respectively. As of

December 31, 2017,

there was

$4.2

million of total unrecognized compensation cost related to employee non-vested stock options. The total unrecognized compensation cost for employee awards will be adjusted for future forfeitures. The Company expects to recognize its remaining stock-based compensation expense over a weighted-average period of

1.95

years.

Employee Stock Purchase Plan

The

2014

ESPP initially authorized the issuance of up to

140,500

shares of Common Stock. The number of shares increases each

January 1,

commencing on

January 1, 2015

and ending on (and including)

January 1, 2024,

by an amount equal to the lesser of

one

percent of the outstanding shares as of the end of the immediately preceding fiscal year,

281,000

shares and any lower amount determined by the Company’s Board of Directors prior to each such

January

1st.

As of

December 31, 2017,

the

2014

ESPP authorized the issuance of up to

304,991

shares of Common Stock. The Company’s Board of Directors has determined there was to be

increase on

January 1, 2018.

The

sixth

offering under the

2014

ESPP began on

July 1, 2017

and ended on

December 31, 2017.

During the years ended

December 31, 2017

and

2016,

100,358

and

4,538

shares, respectively, were issued under the

2014

ESPP resulting in

192,463

shares remaining for future issuance under the plan as of

December 31, 2017.

The Company incurred

$0.1

million and

$0.1

million in stock-based compensation expense related to the

2014

ESPP for the years ended

December 31, 2017

and

2016,

respectively.

Note 11 - Income Taxes

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Income Tax Disclosure [Text Block]

11.

Income Taxes

The components of income from operations before income taxes are as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Domestic	$	(24,803	)	$	(15,860	)	$	(21,377	)
Foreign		(5,161	)		(12,666	)		-
Loss before income taxes	$	(29,964	)	$	(28,526	)	$	(21,377	)

For the years ended

December 31, 2017,

2016,

2015,

the Company has

not

recorded a provision for federal or state income taxes as it has had net operating losses since inception.

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations is as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Income tax benefit using U.S. federal statutory rate	$	(10,186	)	$	(9,696	)	$	(7,315	)
Permanent differences		4			430			260
Stock Compensation - Perm Items		689			-			-
R&D Credit -Perm Items		1,751			1,437			1,310
State income taxes, net of federal benefit		(853	)		(498	)		(808	)
Tax credits		(5,495	)		(4,846	)		(4,219	)
Change in valuation allowance		(54,319	)		8,804			9,782
Foreign rate differential		1,752			4,304			-
Rate change		2,202			-			-
382 Limitation		64,975			-			-
Other		(520	)		65			990
	$	-		$	-		$	-

The significant components of the Company's deferred tax assets are as follows (in thousands):

	Year Ended December 31,
	2017			2015			2014
Net operating loss carryforwards	$	2,651		$	42,156		$	34,488
Federal and state tax credits		2,244			21,223			16,404
Accrued expenses		399			544			27
Patents		191			360			443
Stock-based compensation		1,262			1,353			596
Other		202			320			276
		6,949			65,956			52,234
Valuation allowance		(6,949	)		(65,956	)		(52,234	)
Net deferred tax asset	$	-		$	-		$	-

Management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company's history of operating losses, management of the Company has concluded that it is more likely than

not

that the benefit of its deferred tax assets will

not

be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of

December 31, 2017,

2016,

and

2015.

December 22, 2017,

the President of the United States signed into law the Tax Cuts and Jobs Act (“TCJA”) tax reform legislation. This legislation makes significant changes in U.S. tax law including a reduction in the corporate tax rates, changes to net operating loss carryforwards and carrybacks, and a repeal of the corporate alternative minimum tax. The legislation reduced the U.S. corporate tax rate from the current rate of

34%

21%.

As a result of the enacted law, the Company was required to revalue deferred tax assets and liabilities at the enacted rate. This revaluation resulted in a decrease in net deferred tax asset of

$2.2

million and a corresponding reduction in the valuation allowance against these assets. There is

impact to income tax expense. The other provisions of the Tax Cuts and Jobs Act did

not

have a material impact on the

2017

consolidated financial statements. Our preliminary estimate of the TCJA and the remeasurement of our deferred tax assets and liabilities is subject to the finalization of management’s analysis related to certain matters, such as developing interpretations of the provisions of the TCJA, changes to certain estimates and the filing of our tax returns. U.S. Treasury regulations, administrative interpretations or court decisions interpreting the TCJA

may

require further adjustments and changes in our estimates. The final determination of the TCJA and the remeasurement of our deferred assets and liabilities will be completed as additional information becomes available, but

later than

one

year from the enactment of the TCJA

Net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service (the "IRS") and

may

become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a

three

-year period in excess of

50%

as defined under Sections

382

and

383

in the Internal Revenue Code (

“§382

limitation”). This could substantially limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the Company's value immediately prior to the ownership change. Subsequent ownership changes

may

further affect the limitation in future years. On

August 2, 2017,

the Company completed a financing transaction for

$22.0

million. As a result of this transaction, the company performed a study to review the application of IRC

§382

and

§383

to the Company. It was determined there was an ownership change as of the date of this financing and the Company’s NOLs generated prior to

August 2, 2017

would be fully limited. Therefore, the NOLs and credits generated prior to

August 2, 2017

have been written down to zero. This represents a decrease in Federal NOLs of approximately

$107.3

million (

$34.1

million tax affected) and a decrease in federal credits of

$23.8

million. State NOLs and credits were also fully limited as a result of this ownership change. The state NOLs were reduced by approximately

$5.0

million and credits were reduced by

$2.1

million.

As a result of current year activity, the valuation allowance increased by approximately

$13.1

million during the year ended

December 31, 2017.

This was due primarily to the addition of Orphan Drug Tax credits and the generation of net operating losses. However, this increase was offset by a reduction of

$65.0

million due the

§382

limitation and a reduction of

$2.2

million due to the change in tax rate. Therefore, there was an overall decrease to the valuation allowance of

$54.1

million. The valuation allowance increased by approximately

$8.8

million during the year ended

December 31, 2016,

due primarily to the addition of Orphan Drug Tax credits and the generation of net operating losses. The valuation allowance increased by approximately

$9.8

million during the year ended

December 31, 2015,

due primarily to the addition of Orphan Drug Tax credits and the generation of net operating losses.

Subject to the limitations described above, as of

December 31, 2017,

2016,

and

2015,

the Company has net operating loss carryforwards of approximately

$10.6

million,

$101.4

million, and

$94.2

million, respectively, to offset future federal taxable income, which will expire during

2037.

As of

December 31, 2017,

2016,

and

2015,

the Company has state net operating loss carryforwards of approximately

$6.8

million,

$53.0

million, and

$46.4

million, respectively, to offset future state taxable income, which will expire at various times between

2032

and

2037.

As of

December 31, 2017,

2016

and

2015,

the Company has tax credit carryforwards of approximately

$2.3

million,

$21.8

million and

$16.9

million, respectively, to offset future federal and state income taxes, which will expire at various times between

2022

and

2037.

The Company had

unrecognized tax benefits or related interest and penalties accrued during the years ended

December 31, 2017,

2016,

and

2015.

The Company will recognize interest and penalties related to uncertain tax positions in income tax expense.

The Company is subject to U.S. federal income tax and primarily Massachusetts state income tax. The statute of limitations for assessment by the IRS and state tax authorities is open for tax years ending

December 31, 2014

through

2017,

although carryforward attributes that were generated prior to tax year

2014

may

still be adjusted upon examination by the IRS or state tax authorities if they either have been or will be used in a future period. Currently,

federal or state income tax returns are under examination by the respective taxing authorities.

The Company has adopted ASU

2016

09,

Improvements to Employee Share-Based Payment Accounting, for the quarter ended

March 31, 2017.

As a result of adoption, the deferred tax assets associated with net operating losses were increased by

$0.6

million. These amounts were offset by a corresponding increase in the valuation allowance.

Note 12 - Net Loss Per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Earnings Per Share [Text Block]

12.

Net Loss per Share Attributable to Common Stockholders

As described in Note

Summary of Significant Accounting Policies, the Company computes basic and diluted loss per share using a methodology that gives effect to the impact of outstanding participating securities (the “two-class method”). As the years ended

December 31, 2017,

2016

and

2015

resulted in net losses, there is

income allocation required under the

two

-class method or dilution attributed to weighted-average shares outstanding in the calculation of diluted loss per share.

The following Common Stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect:

	Year Ended December 31,
	2017		2016		2015
Outstanding stock options		2,681,072		2,166,254		2,200,369
Convertible preferred stock		22,112,775		-		-
		24,793,847		2,166,254		2,200,369

Note 13 - Quarterly Financial Information (Unaudited, in Thousands, Except Share and Per Share Data)

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements

Quarterly Financial Information [Text Block]

13.

Quarterly Financial Information (unaudited, in thousands, except share and per share data)

The following table contains selected quarterly financial information from

2017

and

2016.

The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are

not

necessarily indicative of results for any future period.

	Three Months Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Operating expenses	$	6,480		$	5,986		$	12,306		$	5,590
Net loss attributable to common stockholders		(6,498	)		(5,608	)		(19,054	)		(5,551	)
Net loss per share attributable to common stockholders:
Basic and Diluted	$	(0.39	)	$	(0.33	)	$	(1.08	)	$	(0.33	)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders:
Basic and Diluted		16,636,201			17,207,672			17,619,418	(a)		17,619,418

	Three Months Ended
	March 31, 2016			June 30, 2016			September 30, 2016			December 31, 2016
Operating expenses	$	6,819		$	7,854		$	7,166		$	6,866
Net loss attributable to common stockholders		(6,552	)		(7,905	)		(7,107	)		(6,962	)
Net loss per share attributable to common stockholders:
Basic and Diluted	$	(0.40	)	$	(0.48	)	$	(0.43	)	$	(0.42	)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders:
Basic and Diluted		16,507,586			16,561,239			16,582,276			16,595,502

(a) Adjusted to correct an immaterial error in the weighted-average share calculation in the Company's Form

-Q as of

September 30, 2017.

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

At-the-market Equity Offering Program [Policy Text Block]

At-The-Market Equity Offering Program

November 12, 2015,

the Company filed a shelf registration statement on Form S-

$40

million of the Company’s Common Stock at prevailing market prices from time to time. The Registration Statement became effective on

January 12, 2016.

The Company pays Cowen a commission equal to

March 16, 2017

because the Company is currently subject to General Instruction

I.B.6

of Form S-

which limits the amounts that the Company

may

sell under the Registration Statement. For the year ended

December 31, 2017,

the Company sold

896,811

shares of Common Stock under the Sales Agreement for aggregate gross proceeds of

$1.4

million, respectively. For the year ending

December 31, 2017,

total offering costs of

$0.1

million were offset against the proceeds from the sale of common stock.

Convertible Preferred Stock, Policy [Policy Text Block]

Series A Preferred Financing

June 22, 2017,

22,000

shares of the Company’s Series A Convertible Preferred Stock, par value

$0.001

per share (the “Transaction”), for a purchase price of

$1,000

per share, or an aggregate gross purchase price of

$22.0

million, all upon the terms and conditions set forth in the Purchase Agreement. The Company closed this Transaction on

August 2, 2017 (

see Note

August 2, 2017,

the Company entered into a registration rights agreement with the Investors (the “Registration Rights Agreement”). On

August 3, 2017,

in accordance with the Registration Rights Agreement, the Company filed a registration statement on Form S-

to register the common stock issuable upon conversion of the Preferred Shares. The registration statement became effective on

August 21, 2017.

Basis of Presentation, Principles of Consolidation and Use of Estimates

not

may

differ from those estimates or assumptions.

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation, Principles of Consolidation and Use of Estimates

not

may

differ from those estimates or assumptions.

Segment Reporting, Policy [Policy Text Block]

Segment Information

one

operating segment, which is the business of developing and commercializing vonapanitase for the treatment of renal and vascular disease. Currently, the Company operates in only

one

geographic segment.

Fair Value Measurement, Policy [Policy Text Block]

Fair Value of Financial Instruments

The Company’s financial instruments consist of cash and cash equivalents, available-for-sale investments, forward foreign currency contracts (see Note

820,

Fair Value Measurement and Disclosures

not

a measure of the investment credit quality. Fair value measurements are classified and disclosed in

one

of the following

three

categories:

Level

1—Valuations

based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

Level

2—Valuations

based on quoted prices for similar assets or liabilities in markets that are

not

active or for which all significant inputs are observable, either directly or indirectly.

Level

3—Valuations

that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Financial instruments measured at fair value on a recurring basis include cash equivalents, available-for-sale investments and forward foreign currency contracts (see Note

). There have been

changes to the valuation methods utilized by the Company during the years ended

December 31, 2017

and

2016.

The Company evaluates transfers between levels at the end of each reporting period. There were

transfers of financial instruments between levels during the years ended

December 31, 2017

and

2016.

Derivatives, Policy [Policy Text Block]

Derivative Financial Instruments

The Company enters into forward foreign currency contracts to mitigate its exposure to fluctuations in the exchange rates between the Swiss Franc and the U.S. dollar (see Note

not

New Accounting Pronouncements, Policy [Policy Text Block]

Recent Accounting Pronouncements

May 2014,

the FASB issued ASU

2014

09,

“Revenue from Contracts with Customers”

(“ASU

2014

09”

January 1, 2018,

with

early adoption permitted. Earlier application is permitted only as of annual reporting periods beginning after

December 15, 2016,

including interim reporting periods within that reporting period. The amendments

may

be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of initial application. The Company does

not

expect this guidance to have a material impact on its condensed consolidated financial statements, if any.

February 2016,

the FASB issued ASU

2016

02,

Leases (Topic

842

): Amendments to FASB Codification

(“ASU

2016

02”

2016

is effective for public companies for fiscal years, and interim periods within those fiscal years, beginning after

December 15, 2018,

with early adoption permitted. ASU

2016

March 2016,

the FASB issued ASU

2016

09,

Compensation - Stock Compensation (Topic

718

): Improvements to Employee Share-Based Payment Accounting

(“ASU

2016

09”

), which simplifies various aspects of the accounting for share-based payments, including accounting for income taxes, earnings per share, and forfeitures. ASU

2016

is effective for annual periods beginning after

December 15, 2016,

and interim periods within those annual periods with early adoption permitted. The Company adopted ASU

2016

during the quarter ended

March 31, 2017.

As a result of adoption, the deferred tax assets associated with net operating losses increased by

$0.6

August 2016,

the FASB issued ASU

2016

15,

Statement of Cash Flows (Topic

230

): Classification of Certain Cash Receipts and Cash Payments

(“ASU

2016

15”

), which provides clarification regarding how certain cash receipts and cash payment are presented and classified in the statement of cash flows. This update addresses

eight

specific cash flow issues with the objective of reducing the existing diversity in practice. This update is effective for annual and interim periods beginning after

December 15, 2017,

which will require the Company to adopt these provisions in the

first

quarter of fiscal

2019

using a retrospective approach. Early adoption is permitted. The Company does

not

expect the adoption of this guidance to have a material impact on its consolidated financial statements.

May 2017,

the FASB issued ASU

No.

2017

09,

Compensation - Stock Compensation (Topic

718

): Scope of Modification Accounting

(“ASU

2017

09”

2017

09,

an entity will

not

2017

will be applied prospectively to awards modified on or after the adoption date. The guidance is effective for annual periods, and interim periods within those annual periods, beginning after

December 15, 2017.

Early adoption is permitted. The Company is evaluating the impact of the adoption of this guidance on its financial statements but does

not

expect it to have a material impact.

Cash and Cash Equivalents, Policy [Policy Text Block]

Cash and Cash Equivalents

The Company considers all highly liquid investments with maturities of

days or less from the purchase date to be cash equivalents. Cash and cash equivalents are held in depository and money market accounts and are reported at fair value.

Investment, Policy [Policy Text Block]

Short-Term Investments

one

year. There have been

realized gains and losses for the years ended

December 31, 2017,

2016

and

2015.

other-than-temporary declines in value of short-term investments for the years ended

December 31, 2017,

2016

and

2015,

as it is more likely than

not

the Company will hold the securities until maturity or a recovery of the cost basis.

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Concentrations of Credit Risk and Off-Balance Sheet Risk

may

exceed federally insured limits. The Company has

not

experienced any credit losses in such accounts and does

not

believe it is exposed to any significant credit risk on these funds. The Company has

financial instruments with off-balance sheet risk of loss.

Property, Plant and Equipment, Policy [Policy Text Block]

Property and Equipment

Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do

not

Asset	Estimated Useful Life (in years)
Computer equipment and software	3
Furniture, fixtures and other	5
Laboratory equipment	7

Research and Development Expense, Policy [Policy Text Block]

Research and Development Costs

Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]

Stock-Based Compensation Expense

The Company accounts for its stock-based compensation awards to employees and directors in accordance with FASB ASC Topic

718,

Compensation-Stock Compensation

(“ASC

718”

). ASC

718

and FASB ASC Topic

505,

Equity

and are expensed using an accelerated attribution model.

not

expect to pay dividends in the foreseeable future. Refer to Note

“

Use of Estimates

,” for a discussion of the Company's estimated fair value of its Common Stock.

Income Tax, Policy [Policy Text Block]

Income Taxes

Income taxes are recorded in accordance with FASB ASC Topic

740,

“Income Taxes” (“ASC

740”

not

that some or all of the deferred tax assets will

not

be realized. The Company has evaluated available evidence and concluded that the Company

may

not

realize the benefit of its deferred tax assets; therefore, a valuation allowance has been established for the full amount of the deferred tax assets.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC

740.

When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than

not

be realized. The determination as to whether the tax benefit will more likely than

not

be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of

December 31, 2017

and

2016,

the Company did

not

have any significant uncertain tax positions. The Company's practice is to recognize interest and/or penalties related to income tax matters in income tax expense. See Note

for further details.

Earnings Per Share, Policy [Policy Text Block]

Net Income (Loss) per Share Attributable to Common Stockholders

The Company follows the

two

-class method when computing net income (loss) per share in periods when issued shares that meet the definition of participating securities are outstanding. The

two

not

Comprehensive Income, Policy [Policy Text Block]

Comprehensive Loss

Subsequent Events, Policy [Policy Text Block]

Subsequent Events

December 31, 2017

to ensure that this filing includes appropriate disclosure of events both recognized in the consolidated financial statements as of

December 31, 2017

and events which occurred subsequently but were

not

recognized in the consolidated financial statements.

Note 2 - Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Property Plant and Equipment Useful Lives [Table Text Block]

Asset	Estimated Useful Life (in years)
Computer equipment and software	3
Furniture, fixtures and other	5
Laboratory equipment	7

Note 3 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

	As of December 31, 2017
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	11,662	$	-	$	-	$	11,662
Government securities		20,971		-		-		20,971
Total	$	32,633	$	-	$	-	$	32,633

	As of December 31, 2016
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	28,876	$	-	$	-	$	28,876
Government securities		4,925		-		-		4,925
Total	$	33,801	$	-	$	-	$	33,801

Available-for-sale Securities [Table Text Block]

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2017
Government securities
(Due within 1 year)	$	20,991	$	-	$	(20	)	$	20,971
	$	20,991	$	-	$	(20	)	$	20,971

December 31, 2016
Government securities
(Due within 1 year)	$	4,924	$	1	$	-		$	4,925
	$	4,924	$	1	$	-		$	4,925

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Note 5 - Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Property, Plant and Equipment [Table Text Block]

	As of December 31,
	2017			2016

Computer equipment and software	$	192		$	141
Furniture, fixtures, and other		302			318
Laboratory equipment		477			478
		971			937
Accumulated depreciation		(712	)		(565	)
Property and equipment, net	$	259		$	372

Note 6 - Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Accrued Liabilities [Table Text Block]

	As of December 31,
	2017		2016

Payroll and employee-related costs	$	1,318	$	1,139
Contracted service costs		7,218		2,891
Professional fees and other		413		493
Total	$	8,949	$	4,523

Note 7 - Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]

Year Ending December 31:	Amount

2018	$	270
2019		207
Total minimum lease payments	$	477

Note 9 - Common Stock (Tables)	12 Months Ended
Note 9 - Common Stock (Tables)	Dec. 31, 2017
Notes Tables
Common Stock Reserved for Future Issuance [Table Text Block]	<div style="display: inline; font-family: times new roman; font-size: 10pt"><table cellpadding="0" cellspacing="0" style="border-collapse: collapse; min-; min-width: 700px;"> <tr style="vertical-align: bottom"> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt"> </td> <td colspan="3" style="font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">December 31,</td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt"> </td> <td colspan="3" style="font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">December 31,</td> </tr> <tr style="vertical-align: bottom"> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt"> </td> <td colspan="3" style="font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2017</td> <td style="font-size: 10pt; font-weight: bold; padding-bottom: 1pt"> </td> <td colspan="3" style="font-size: 10pt; font-weight: bold; text-align: center; border-bottom: Black 1pt solid">2016</td> </tr> <tr style="vertical-align: bottom"> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt"> </td> <td colspan="3" style="font-size: 10pt; text-align: center"> </td> <td> </td> <td colspan="3"> </td> </tr> <tr style="vertical-align: bottom; background-color: rgb(204,238,255)"> <td style="width: 70%; font-size: 10pt; text-align: left">Conversion of Series A Preferred Stock</td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">22,112,775</div></td> <td style="width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 1%; font-size: 10pt"> </td> <td style="width: 1%; font-size: 10pt; text-align: left"> </td> <td style="width: 12%; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">-</div></td> <td style="width: 1%; font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: White"> <td style="font-size: 10pt; text-align: left">Stock-based compensation awards</td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">3,572,457</div></td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt"> </td> <td style="font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">2,982,470</div></td> <td style="font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: rgb(204,238,255)"> <td style="font-size: 10pt; text-align: left; padding-bottom: 1pt">Employee Stock Purchase Plan</td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">192,463</div></td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; padding-bottom: 1pt"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">292,821</div></td> <td style="border-bottom: Black 1pt solid; font-size: 10pt; text-align: left"> </td> </tr> <tr style="vertical-align: bottom; background-color: White"> <td style="font-size: 10pt; padding-bottom: 2.25pt">Total</td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">25,877,695</div></td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="font-size: 10pt; padding-bottom: 2.25pt"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: right"><div style="display: inline; font-style: italic; font-weight: inherit; font-style: normal;">3,275,291</div></td> <td style="border-bottom: Black 2.25pt double; font-size: 10pt; text-align: left"> </td> </tr> </table></div>

Note 10 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Year Ended December 31,
	2017		2016		2015

Research and development	$	1,109	$	1,114	$	650
General and administrative		2,118		2,229		1,514
Total	$	3,227	$	3,343	$	2,164

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year Ended December 31,
	2017			2016			2015
Weighted average expected volatility		94.5	%		84.4	%		79.8	%
Expected term (in years)		6.06			6.05			6.11
Risk free interest rate		2.09	%		1.45	%		1.76	%
Expected dividend yield		0	%		0	%		0	%

Share-based Compensation, Stock Options, Activity [Table Text Block]

	Options			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value

Outstanding at December 31, 2016		2,166,254		$	8.55		7.1	$	124
Granted		719,337		$	1.99
Exercised		(74,001	)	$	1.45
Forfeited		(30,272	)	$	10.69
Expired		(100,246	)	$	2.60
Outstanding at December 31, 2017		2,681,072		$	7.18		6.8	$	121
Exercisable at December 31, 2017		1,495,789		$	8.18		5.9	$	85
Vested or expected to vest at December 31, 2017 (1)		2,681,072		$	7.18		6.8	$	121

Note 11 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]

	Year Ended December 31,
	2017			2016			2015
Domestic	$	(24,803	)	$	(15,860	)	$	(21,377	)
Foreign		(5,161	)		(12,666	)		-
Loss before income taxes	$	(29,964	)	$	(28,526	)	$	(21,377	)

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	Year Ended December 31,
	2017			2016			2015
Income tax benefit using U.S. federal statutory rate	$	(10,186	)	$	(9,696	)	$	(7,315	)
Permanent differences		4			430			260
Stock Compensation - Perm Items		689			-			-
R&D Credit -Perm Items		1,751			1,437			1,310
State income taxes, net of federal benefit		(853	)		(498	)		(808	)
Tax credits		(5,495	)		(4,846	)		(4,219	)
Change in valuation allowance		(54,319	)		8,804			9,782
Foreign rate differential		1,752			4,304			-
Rate change		2,202			-			-
382 Limitation		64,975			-			-
Other		(520	)		65			990
	$	-		$	-		$	-

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	Year Ended December 31,
	2017			2015			2014
Net operating loss carryforwards	$	2,651		$	42,156		$	34,488
Federal and state tax credits		2,244			21,223			16,404
Accrued expenses		399			544			27
Patents		191			360			443
Stock-based compensation		1,262			1,353			596
Other		202			320			276
		6,949			65,956			52,234
Valuation allowance		(6,949	)		(65,956	)		(52,234	)
Net deferred tax asset	$	-		$	-		$	-

Note 12 - Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	Year Ended December 31,
	2017		2016		2015
Outstanding stock options		2,681,072		2,166,254		2,200,369
Convertible preferred stock		22,112,775		-		-
		24,793,847		2,166,254		2,200,369

Note 13 - Quarterly Financial Information (Unaudited, in Thousands, Except Share and Per Share Data) (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Quarterly Financial Information [Table Text Block]

	Three Months Ended
	March 31, 2017			June 30, 2017			September 30, 2017			December 31, 2017
Operating expenses	$	6,480		$	5,986		$	12,306		$	5,590
Net loss attributable to common stockholders		(6,498	)		(5,608	)		(19,054	)		(5,551	)
Net loss per share attributable to common stockholders:
Basic and Diluted	$	(0.39	)	$	(0.33	)	$	(1.08	)	$	(0.33	)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders:
Basic and Diluted		16,636,201			17,207,672			17,619,418	(a)		17,619,418

	Three Months Ended
	March 31, 2016			June 30, 2016			September 30, 2016			December 31, 2016
Operating expenses	$	6,819		$	7,854		$	7,166		$	6,866
Net loss attributable to common stockholders		(6,552	)		(7,905	)		(7,107	)		(6,962	)
Net loss per share attributable to common stockholders:
Basic and Diluted	$	(0.40	)	$	(0.48	)	$	(0.43	)	$	(0.42	)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders:
Basic and Diluted		16,507,586			16,561,239			16,582,276			16,595,502

Note 1 - Organization and Operations (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents, and Short-term Investments	$ 42,100
Retained Earnings (Accumulated Deficit)	$ (189,741)	$ (159,777)

Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Aug. 02, 2017	Nov. 12, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017
Preferred Stock, Par or Stated Value Per Share			$ 0.001	$ 0.001
Number of Operating Segments			1
Number of Reportable Segments			1
Deferred Tax Assets, Operating Loss Carryforwards			$ 2,651	$ 42,156	$ 34,488
Available-for-sale Securities, Gross Realized Gain (Loss)			0	0	0
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities			0	0	0
Liability for Uncertainty in Income Taxes, Current			0	0
Deferred Tax Assets, Valuation Allowance			$ 6,949	$ 65,956	$ 52,234
Accounting Standards Update 2016-09 [Member]
Deferred Tax Assets, Operating Loss Carryforwards						$ 600
Deferred Tax Assets, Valuation Allowance						$ 600
Series A Convertible Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues	22,000
Payments of Stock Issuance Costs	$ 500
Preferred Stock, Par or Stated Value Per Share	$ 0.001		$ 0.001	$ 0.001
Shares Issued, Price Per Share	$ 1,000
Proceeds from Issuance of Convertible Preferred Stock	$ 22,000
Common Stock [Member]
Stock Issued During Period, Shares, New Issues			896,811
Sales Agreement [Member] \| Cowen and Company, LLC [Member] \| Common Stock [Member]
Sale of Stock, Maximum Value of Stock Offered		$ 40,000
Sale of Stock, Commission to Sales Agent, Percentage			3.00%
Stock Issued During Period, Shares, New Issues			896,811
Proceeds from Issuance of Common Stock			$ 1,400
Payments of Stock Issuance Costs			$ 100

Note 2 - Summary of Significant Accounting Policies - Property and Equipment Useful Lives (Details)	12 Months Ended
	Dec. 31, 2017
Computer Equipment and Software [Member]
Property and equipment, useful life (Year)	3 years
Furniture and Fixtures [Member]
Property and equipment, useful life (Year)	5 years
Laboratory Equipment [Member]
Property and equipment, useful life (Year)	7 years

Note 3 - Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Total	$ 32,633	$ 33,801
Cash Equivalents [Member]
Cash equivalents	11,662	28,876
US Government Agencies Debt Securities [Member]
Government securities	20,971	4,925
Fair Value, Inputs, Level 1 [Member]
Total	32,633	33,801
Fair Value, Inputs, Level 1 [Member] \| Cash Equivalents [Member]
Cash equivalents	11,662	28,876
Fair Value, Inputs, Level 1 [Member] \| US Government Agencies Debt Securities [Member]
Government securities	20,971	4,925
Fair Value, Inputs, Level 2 [Member]
Total
Fair Value, Inputs, Level 2 [Member] \| Cash Equivalents [Member]
Cash equivalents
Fair Value, Inputs, Level 2 [Member] \| US Government Agencies Debt Securities [Member]
Government securities
Fair Value, Inputs, Level 3 [Member]
Total
Fair Value, Inputs, Level 3 [Member] \| Cash Equivalents [Member]
Cash equivalents
Fair Value, Inputs, Level 3 [Member] \| US Government Agencies Debt Securities [Member]
Government securities

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References + Details

Note 3 - Fair Value Measurements - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized Cost	$ 20,991	$ 4,924
Unrealized Gains		1
Unrealized Losses	(20)
Fair Value	20,971	4,925
US Government Agencies Debt Securities [Member]
Amortized Cost	20,991	4,924
Unrealized Gains		1
Unrealized Losses	(20)
Fair Value	$ 20,971	$ 4,925

Note 5 - Property and Equipment, Net (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Depreciation	$ 148	$ 123	$ 57

Note 5 - Property and Equipment, Net - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property and equipment	$ 971	$ 937
Accumulated depreciation	(712)	(565)
Property and equipment, net	259	372
Computer Equipment and Software [Member]
Property and equipment	192	141
Furniture and Fixtures [Member]
Property and equipment	302	318
Laboratory Equipment [Member]
Property and equipment	$ 477	$ 478

Note 6 - Accrued Expenses - Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payroll and employee-related costs	$ 1,318	$ 1,139
Contracted service costs	7,218	2,891
Professional fees and other	413	493
Total	$ 8,949	$ 4,523

Note 7 - Commitments and Contingencies (Details Textual) SFr in Millions	1 Months Ended			12 Months Ended
	Jun. 30, 2018	Aug. 31, 2017 ft²	Feb. 28, 2002	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 CHF (SFr)
Royalty Payment, Percentage of Net Sales			2.50%
Operating Leases, Increase in Office Space \| ft²		2,552
Area of Real Estate Property \| ft²		7,500
Lessee, Operating Lease, Renewal Term		1 year
Operating Leases, Notice Required to Extend Term		180 days
Operating Leases, Rent Expense				$ 200,000	$ 200,000	$ 200,000
Security Deposit				22,000
Letters of Credit Outstanding, Amount				22,000	14,000
Loans Pledged as Collateral				22,000	$ 14,000
Scenario, Forecast [Member]
Lessee, Operating Lease, Term of Contract	1 year 90 days
Inventories, Four Batches [Member]
Purchase Commitment, Amount Executed				$ 7,800,000			SFr 7.6

Note 7 - Commitments and Contingencies - Future Minimum Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
2018	$ 270
2019	207
Total minimum lease payments	$ 477

Note 8 - Series A Preferred Financing (Details Textual) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Aug. 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Preferred Stock, Par or Stated Value Per Share		$ 0.001	$ 0.001
Accretion of Redeemable Convertible Preferred Stock to Redemption Value		$ 6,747
Series A Convertible Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues	22,000
Preferred Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001	$ 0.001
Shares Issued, Price Per Share	$ 1,000
Proceeds from Issuance of Convertible Preferred Stock	$ 22,000
Payments of Stock Issuance Costs	$ 500
Convertible Preferred Stock, Shares Issued upon Conversion	1,005
Convertible Preferred Stock, Conversion Price of Shares Issued upon Conversion	$ 0.9949
Convertible Preferred Stock, Maximum Ownership Percentage Allowed after Conversion of Stock	9.985%
Preferred Stock, Redemption Price Per Share	$ 1.30
Accretion of Redeemable Convertible Preferred Stock to Redemption Value	$ 6,700
Preferred Stock, Liquidation Preference Per Share		$ 0.001

Note 9 - Common Stock (Details Textual) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Common Stock, Shares Authorized	100,000,000	100,000,000
Common Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Common Stock, Shares, Issued	17,674,729	16,603,559
Common Stock, Shares, Outstanding	17,674,729	16,603,559

Note 9 - Common Stock - Common Stock Reserved for Future Issuance (Details) - shares	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Reserved for future issuance (in shares)	25,877,695	3,275,291
The 2014 Employee Stock Purchase Plan [Member]
Reserved for future issuance (in shares)	192,463	292,821	140,500
Performance Shares [Member]
Reserved for future issuance (in shares)	3,572,457	2,982,470
Conversion of Series A Preferred Stock to Common Stock [Member]
Reserved for future issuance (in shares)	22,112,775

Note 10 - Stock-based Compensation (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	5 years 328 days
Allocated Share-based Compensation Expense	$ 3,227,000	$ 3,343,000	$ 2,164,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	719,337	132,495	1,010,256
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 1.99	$ 5.08	$ 9.34
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 1.99	$ 7.11
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 27,000	$ 600,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	$ 4,200,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 346 days
Common Stock, Capital Shares Reserved for Future Issuance	25,877,695	3,275,291
Employee Stock Option [Member] \| Non-Employees [Member]
Allocated Share-based Compensation Expense	$ 0	$ 0	$ 2,000
The 2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	704,000
Share-based Compensation Arrangement by Share-based Payment Award Number of Annual Additional Shares Percentage	4.00%
The 2014 Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
The 2014 Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
The 2006 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	10 years
The 2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	304,991
Share-based Compensation Arrangement by Share-based Payment Award Number of Annual Additional Shares Percentage	1.00%
Allocated Share-based Compensation Expense	$ 100,000	$ 100,000
Common Stock, Capital Shares Reserved for Future Issuance	192,463	292,821		140,500
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	100,358	4,538
The 2014 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	281,000

Note 10 - Stock-based Compensation - Stock-based Compensation Expense Recognized for Stock Options Granted (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allocated share-based compensation	$ 3,227	$ 3,343	$ 2,164
Research and Development Expense [Member]
Allocated share-based compensation	1,109	1,114	650
General and Administrative Expense [Member]
Allocated share-based compensation	$ 2,118	$ 2,229	$ 1,514

Note 10 - Stock-based Compensation - Black-scholes Valuation Assumptions (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted average expected volatility	94.50%	84.40%	79.80%
Expected term (in years) (Year)	6 years 21 days	6 years 18 days	6 years 40 days
Risk free interest rate	2.09%	1.45%	1.76%
Expected dividend yield	0.00%	0.00%	0.00%

Note 10 - Stock-based Compensation - Stock Option Activity for Employees and Non-employees (Details) - USD ($)
$ / shares in Units, $ in Thousands

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Options Outstanding, Beginning Balance (in shares)

2,166,254

Options Outstanding, Weighted Average Exercise Price, Beginning Balance (in dollars per share)

$ 8.55

Options Outstanding, Weighted-average Remaining Contractual Term, Beginning Balance (Year)

6 years 292 days

7 years 36 days

Options Outstanding, Aggregate Intrinsic Value, Beginning Balance

$ 121

$ 124

Options Granted (in shares)

719,337

132,495

1,010,256

Options Granted, Weighted Average Exercise Price (in dollars per share)

$ 1.99

$ 7.11

Options Exercised (in shares)

(74,001)

Options Exercised, Weighted Average Exercise Price (in dollars per share)

$ 1.45

Options Forfeited (in shares)

(30,272)

Options Forfeited, Weighted Average Exercise Price (in dollars per share)

$ 10.69

Options Expired (in shares)

(100,246)

Options Expired, Weighted Average Exercise Price (in dollars per share)

$ 2.60

Options Outstanding, Ending Balance (in shares)

2,681,072

2,166,254

Options Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share)

$ 7.18

$ 8.55

Options Exercisable (in shares)

1,495,789

Options Exercisable, Weighted Average Exercise Price (in dollars per share)

$ 8.18

Options Exercisable, Weighted-average Remaining Contractual Term (Year)

5 years 328 days

Options Exercisable, Aggregate Intrinsic Value

$ 85

Options Vested or Expected to Vest (in shares)

^[1]

2,681,072

Options Vested or Expected to Vest, Weighted Average Exercise Price (in dollars per share)

^[1]

$ 7.18

Options Vested or Expected to Vest, Weighted-average Remaining Contractual Term (Year)

^[1]

6 years 292 days

Options Vested or Expected to Vest, Aggregate Intrinsic Value

^[1]

$ 121

[1]	Represents the number of vested options at December 31, 2017 plus the number of unvested options expected to vest based on the unvested options outstanding at December 31, 2017.

Note 11 - Income Taxes (Details Textual) - USD ($) $ in Thousands		12 Months Ended
	Aug. 02, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			34.00%
Deferred Tax Assets, Increase (Decrease) from Revaluation Due to Tax Rate Change			$ (2,200)
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability			0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(54,100)	$ 8,800	$ 9,800
Operating Loss Carryforwards	$ 0
Tax Credit Carryforward, Amount	0		2,300	21,800	16,900
Unrecognized Tax Benefits			0	0	0
Deferred Tax Assets, Valuation Allowance			6,949	65,956	52,234
Deferred Tax Assets, Valuation Allowance, Increase (Decrease) from Revaluation Due to Tax Rate Change			(2,200)
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense			0	0	0
Deferred Tax Assets, Operating Loss Carryforwards			2,651	42,156	34,488
Accounting Standards Update 2016-09 [Member]
Deferred Tax Assets, Valuation Allowance						$ 600
Deferred Tax Assets, Operating Loss Carryforwards						$ 600
Current Year Deferred Tax Assets Activity [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			13,100
Effect on Deferred Tax Assets of Section 382 Limitation [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(65,000)
Effect of Tax Rate Change on Deferred Tax Assets [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(2,200)
Series A Preferred Stock [Member]
Proceeds from Issuance of Convertible Preferred Stock	22,000
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%
Domestic Tax Authority [Member]
Income Tax Expense (Benefit)			0	0	0
Operating Loss Carryforwards			10,600	101,400	94,200
Domestic Tax Authority [Member] \| Internal Revenue Service (IRS) [Member]
Decrease in Net Operating Loss Carryforwards from Section 382 Limitation	107,300
Decrease in Net Operating Loss Carryforwards from Section 382 Limitation, Tax Affected	34,100
Decrease in Tax Credit Carryforward Amount from Section 382 Limitation	23,800
State and Local Jurisdiction [Member]
Income Tax Expense (Benefit)			0	0	0
Decrease in Net Operating Loss Carryforwards from Section 382 Limitation	5,000
Decrease in Tax Credit Carryforward Amount from Section 382 Limitation	$ 2,100
Operating Loss Carryforwards			$ 6,800	$ 53,000	$ 46,400

Note 11 - Income Taxes - Domestic and Foreign Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Domestic	$ (24,803)	$ (15,860)	$ (21,377)
Foreign	(5,161)	(12,666)
Loss before income taxes	$ (29,964)	$ (28,526)	$ (21,377)

Note 11 - Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income tax benefit using U.S. federal statutory rate	$ (10,186)	$ (9,696)	$ (7,315)
Permanent differences	4	430	260
Stock Compensation - Perm Items	689
R&D Credit -Perm Items	1,751	1,437	1,310
State income taxes, net of federal benefit	(853)	(498)	(808)
Tax credits	(5,495)	(4,846)	(4,219)
Change in valuation allowance	(54,319)	8,804	9,782
Foreign rate differential	1,752	4,304
Rate change	2,202
382 Limitation	64,975
Other	$ (520)	$ 65	$ 990

Note 11 - Income Taxes - Summary of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets, Operating Loss Carryforwards	$ 2,651	$ 42,156	$ 34,488
Federal and state tax credits	2,244	21,223	16,404
Accrued expenses	399	544	27
Patents	191	360	443
Stock-based compensation	1,262	1,353	596
Other	202	320	276
	6,949	65,956	52,234
Valuation allowance	(6,949)	(65,956)	(52,234)
Net deferred tax asset	$ 0	$ 0	$ 0

Note 12 - Net Loss Per Share Attributable to Common Stockholders - Common Stock Equivalents Excluded From Calculation of Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities (in shares)	24,793,847	2,166,254	2,200,369
Convertible Preferred Stock [Member]
Antidilutive Securities (in shares)	22,112,775
Employee Stock Option [Member]
Antidilutive Securities (in shares)	2,681,072	2,166,254	2,200,369

Note 13 - Quarterly Financial Information (Unaudited, in Thousands, Except Share and Per Share Data) - Quarterly Financial Information (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2016

Sep. 30, 2016

Jun. 30, 2016

Mar. 31, 2016

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Total operating expenses

$ 5,590

$ 12,306

$ 5,986

$ 6,480

$ 6,866

$ 7,166

$ 7,854

$ 6,819

$ 30,362

$ 28,705

$ 20,870

Net loss attributable to common stockholders

$ (5,551)

$ (19,054)

$ (5,608)

$ (6,498)

$ (6,962)

$ (7,107)

$ (7,905)

$ (6,552)

Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)

$ (0.33)

$ (1.08)

$ (0.33)

$ (0.39)

$ (0.42)

$ (0.43)

$ (0.48)

$ (0.40)

$ (2.13)

$ (1.72)

$ (1.30)

Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)

17,619,418

^[1]

17,207,672

16,636,201

16,595,502

16,582,276

16,561,239

16,507,586

17,274,326

16,561,799

16,464,123

[1]	Adjusted to correct an immaterial error in the weighted-average share calculation in the Company's Form 10-Q as of September 30, 2017.