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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Face amount or stated value per share of common stock.

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

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The cash inflow associated with the amount received from entity's raising of capital via private rather than public placement.

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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			3 Months Ended	6 Months Ended
	Feb. 06, 2019	Jul. 19, 2016	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Common Stock
Common stock, par value (in dollars per share)			$ 0.001	$ 0.001		$ 0.001
Accumulated deficit			$ (210,473)	$ (210,473)		$ (197,304)
Cash, cash equivalents and short-term investments			$ 46,100	$ 46,100
Common stock
Common Stock
Number of shares issued			49,495	403,241	539,026
Additional common stock issued			$ 1	$ 1	$ 1
Common stock \| Cowen
Common Stock
Percentage of commission paid to underwriter based on proceeds from common stock		3.00%
Common stock \| ATM
Common Stock
Number of shares issued				403,241
Share price (in dollars per share)			$ 6.17	$ 6.17
Net proceeds				$ 2,200
Common stock \| First ATM Program \| Cowen
Common Stock
Remaining current sales agreement		$ 49,600
Common stock \| February 2019 Financing \| Oppenheimer & Co. Inc
Common Stock
Number of shares issued	4,000,000
Number of warrants issued	2,000,000
Warrants price (in dollars per unit)	$ 5.00
Proceeds from public offering, net of issuance costs	$ 18,500