Percentage of commission paid to underwriters based on proceeds from offering.

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Amount of remaining available under its current sales agreement.

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It represents the warrant purchase price per share.

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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of securities into which each warrant or right may be converted. For example, but not limited to, each warrant may be converted into two shares.

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The cash inflow from the additional capital contribution to the entity.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Per share or per unit amount of equity securities issued.

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Number of new stock issued during the period.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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Organization and Operations - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended	12 Months Ended
	Jan. 30, 2020	Feb. 06, 2019	Jun. 19, 2018	Jul. 19, 2016	Jan. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity
Gross proceeds from public offering						$ 6,996	$ 8,363
Accumulated deficit						(223,597)	$ (197,304)
Cash, cash equivalents and short-term investments						$ 36,200
Common stock
Stockholders' Equity
Number of shares issued						1,282,904	577,195
Gross proceeds from public offering						$ 1	$ 1
Common stock \| Cowen
Stockholders' Equity
Percentage of commission paid to underwriter based on proceeds from common stock				3.00%
Common stock \| ATM
Stockholders' Equity
Number of shares issued						1,282,904
Share price (in dollars per share)						$ 5.81
Gross proceeds from public offering						$ 7,500
Proceeds from public offering, net of issuance costs						$ 7,000
Common stock \| First ATM Program \| Cowen
Stockholders' Equity
Remaining available under sales agreement				$ 43,600
Common stock \| February 2019 Financing \| Oppenheimer & Co. Inc
Stockholders' Equity
Number of shares issued		4,000,000	4,200,000
Share price (in dollars per share)			$ 0.001
Number of warrants issued		2,000,000	4,200,000
Warrants price (in dollars per unit)		$ 5.00	$ 10.00
Gross proceeds from public offering			$ 42,000
Proceeds from public offering, net of issuance costs		$ 18,500	$ 38,900
Common stock \| January 2020 Financing \| Oppenheimer & Co. Inc
Stockholders' Equity
Share price (in dollars per share)	$ 5.00
Gross proceeds from public offering	$ 26,500
Subsequent Events \| ATM
Stockholders' Equity
Number of shares issued					173,572
Share price (in dollars per share)					$ 6.29
Gross proceeds from public offering					$ 1,100
Subsequent Events \| 2020 Equity financings
Stockholders' Equity
Proceeds from public offering, net of issuance costs					$ 25,600
Subsequent Events \| Common stock \| Over-Allotment option for underwriters \| Oppenheimer & Co. Inc
Stockholders' Equity
Number of shares issued	690,000
Subsequent Events \| Common stock \| January 2020 Financing \| Oppenheimer & Co. Inc
Stockholders' Equity
Number of shares issued	5,290,000
Proceeds from public offering, net of issuance costs	$ 24,500