Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]	Total
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
Stock option exercises	$ 1	528			529
Stock option exercises, shares	283,250
Vesting of restricted stock units, net
Vesting of restricted stock units, net, shares	100,912
Shares withheld for tax withholding		(740)			(740)
Shares withheld for tax withholding, shares	(82,011)
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
Balance at Dec. 31, 2019	$ 27	474,174	72	(435,357)	38,916
Balance, shares at Dec. 31, 2019	27,374,653
Stock-based compensation expense		3,221			3,221
Stock-based compensation expense, shares
Stock option exercises		31			31
Stock option exercises, shares	10,000
Vesting of restricted stock units, net
Vesting of restricted stock units, net, shares	158,513
Shares withheld for tax withholding		(5)			(5)
Shares withheld for tax withholding, shares	(4,587)
Other comprehensive income			(69)		(69)
Issuance of common stock, net of issuance costs of $1.3 million	$ 11	12,588			12,599
Issuance of common stock, net of issuance costs of $1.3 million, shares	10,854,710
Net loss				(13,040)	(13,040)
Balance at Mar. 31, 2020	$ 38	$ 490,009	$ 3	$ (448,397)	$ 41,653
Balance, shares at Mar. 31, 2020	38,393,289