Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Preferred Stock Series B convertible preferred stock	Preferred Stock Series C convertible preferred stock	Preferred Stock Series D convertible preferred stock April 2018 institutional sale of convertible preferred stock and warrants, net of issuance costs	Preferred Stock Series D convertible preferred stock	Preferred Stock Series E convertible preferred stock Issuance of series E convertible preferred stock	Preferred Stock Series E convertible preferred stock	Common Stock 2019 private placement	Common Stock Issuance of series E convertible preferred stock	Common Stock 2018 institutional sales of common stock and warrants, net of issuance costs	Common Stock September 2018 public offering	Common Stock At The Market Offering	Common Stock	Additional Paid-in Capital 2019 private placement	Additional Paid-in Capital Issuance of series E convertible preferred stock	Additional Paid-in Capital April 2018 institutional sale of convertible preferred stock and warrants, net of issuance costs	Additional Paid-in Capital 2018 institutional sales of common stock and warrants, net of issuance costs	Additional Paid-in Capital September 2018 public offering	Additional Paid-in Capital At The Market Offering	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	2019 private placement	April 2018 institutional sale of convertible preferred stock and warrants, net of issuance costs	2018 institutional sales of common stock and warrants, net of issuance costs	September 2018 public offering	At The Market Offering	Total
Balance at Dec. 31, 2017		$ 1																	$ 411,125	$ (334,759)							$ 76,367
Balance (in shares) at Dec. 31, 2017	6,055	95,388										123
Changes in Stockholders' (Deficit) Equity
Net loss																				(81,152)							(81,152)
Stock-based compensation expense																			3,098								3,098
Down round adjustments for convertible preferred stock and warrants																			3,079	(3,079)
Stock issued															$ 5,081	$ 14,316	$ 447	$ 13,385					$ 5,081	$ 14,316	$ 447	$ 13,385
Stock issued (in shares)			6,000						5,768	696	52,197
Redemption of stock																			(500)								500
Redemption of stock (in shares)				(500)
Conversion of stock (in shares)	(5,896)			(5,500)								4,873
Issuance of common stock upon exercise of warrants																			621								621
Issuance of common stock upon exercise of warrants (in shares)												9,435
Balance at Dec. 31, 2018		$ 1																	450,652	(418,990)							31,663
Balance (in shares) at Dec. 31, 2018	159	95,388										73,092
Changes in Stockholders' (Deficit) Equity
Net loss																				(74,207)							(74,207)
Other comprehensive income (loss), net of tax																					$ (8)						(8)
Stock-based compensation expense																			2,311								2,311
Warrant expense																			130								130
Stock issued													$ 434									$ 434
Stock issued (in shares)							199,167
Warrant adjustment																			(312)								312
Conversion of stock					$ 12	$ (12)								$ (12)					12
Conversion of stock (in shares)	(156)				1,192,000	(1,192,000)		(9,933)				10,973
Warrant liability reclassified to equity																			63,954								63,954
Issuance of common stock upon exercise of warrants																			142								142
Issuance of common stock upon exercise of warrants (in shares)												118,440
Balance at Dec. 31, 2019		$ 1																	$ 517,311	$ (493,197)	$ (8)						$ 24,107
Balance (in shares) at Dec. 31, 2019	3	95,388										391,739