Restatement of Consolidated Financial Statements - Impact on Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Warrant liability	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Total liabilities	51,380	54,052	56,295	22,528	19,924	19,918	20,822	20,675
Additional paid-in-capital	197,853	196,853	195,906	195,661	195,483	195,142	194,759	194,208
Accumulated deficit	(219,984)	(214,036)	(204,540)	(196,244)	(188,893)	(185,213)	(176,718)	(168,429)
Total stockholders' (deficit) equity	(22,283)	(17,335)	(8,786)	(735)	6,438	9,777	17,889	25,627	$ (1,716)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Warrant liability	1,504	10,270	11,430	1,628	1,240	12,073	13,537	14,248
Total liabilities	52,884	64,322	67,725	24,156	21,164	31,991	34,359	34,923
Additional paid-in-capital	180,047	179,047	178,100	177,855	177,677	177,336	176,953	176,402
Accumulated deficit	(203,682)	(206,500)	(198,164)	(180,066)	(172,327)	(179,480)	(172,449)	(164,871)
Total stockholders' (deficit) equity	(23,787)	(27,605)	(20,216)	(2,363)	5,198	(2,296)	4,352	11,379
Misapplication of Accounting Guidance for Warrants \| Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Warrant liability	(1,504)	(10,270)	(11,430)	(1,628)	(1,240)	(12,073)	(13,537)	(14,248)
Total liabilities	(1,504)	(10,270)	(11,430)	(1,628)	(1,240)	(12,073)	(13,537)	(14,248)
Additional paid-in-capital	17,806	17,806	17,806	17,806	17,806	17,806	17,806	17,806
Accumulated deficit	(16,302)	(7,536)	(6,376)	(16,178)	(16,566)	(5,733)	(4,269)	(3,558)
Total stockholders' (deficit) equity	$ 1,504	$ 10,270	$ 11,430	$ 1,628	$ 1,240	$ 12,073	$ 13,537	$ 14,248

Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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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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Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.

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

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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