Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]	Total
Balance at Dec. 31, 2017	$ 109,104	$ 7	$ 157,395		$ (269,920)	$ (3,414)
Balance, shares at Dec. 31, 2017	1,656,838	7,082,836
Conversion of Series A preferred stock to common stock	$ (391)		391
Conversion of Series A preferred stock to common stock, shares	(1,602,099)	363,036
Conversion of Series B preferred stock to common stock	$ (4,020)	$ 1	4,019
Conversion of Series B preferred stock to common stock, shares	(47,689)	794,820
Conversion of Series E preferred stock to common stock	$ (104,693)	$ 7	104,686
Conversion of Series E preferred stock to common stock, shares	(7,050)	7,050,000
Exchange of Series F preferred stock and dividends to common stock		$ 1	13,060			13,061
Exchange of Series F preferred stock and dividends to common stock, shares		1,003,393
Extinguishment of warrant liability			3,045			3,045
Extinguishment of warrant liability, shares		151,871
Stock-based compensation expense			7,445			7,445
Stock-based compensation expense, shares
Deemed dividend - accretion of discount on Series F preferred stock			(698)			(698)
Cumulative dividends on Series F preferred stock			(191)			(191)
Series F preferred stock dividends paid in common stock			306			306
Series F preferred stock dividends paid in common stock, shares		11,708
Net loss					(11,777)	(11,777)
Balance at Mar. 31, 2018		$ 16	289,458		(281,697)	7,777
Balance, shares at Mar. 31, 2018		16,457,664
Balance at Dec. 31, 2018		$ 21	414,840	36	(342,864)	72,033
Balance, shares at Dec. 31, 2018		21,447,088
Stock-based compensation expense			10,327			10,327
Stock-based compensation expense, shares
Deemed dividend - accretion of discount on Series F preferred stock
Cumulative dividends on Series F preferred stock
Series F preferred stock dividends paid in common stock
Stock option exercises, net		$ 1	1,126			1,127
Stock option exercises, net shares		228,937
Vesting of restricted stock units, net
Vesting of restricted stock units, net, shares		73,214
Shares withheld for tax withholding on vesting of restricted stock			(1,338)			(1,338)
Other comprehensive income				17		17
Net loss					(25,573)	(25,573)
Balance at Mar. 31, 2019		$ 22	$ 424,955	$ 53	$ (368,437)	$ 56,593
Balance, shares at Mar. 31, 2019		21,749,239