Condensed Consolidated Statement of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at Dec. 31, 2018	$ (48,045)	$ 41	$ 341,284	$ (389,370)
Beginning balance, shares at Dec. 31, 2018		40,936,735
Issuance of common stock upon exercise of stock options, value	120		120
Issuance of common stock upon exercise of stock options, shares		38,125
Issuance of common stock upon vesting of RSUs, net of tax withholdings	153		153
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		73,500
Issuance of common stock under ESPP plan, value	207		207
Issuance of common stock under ESPP plan, shares		46,472
Stock-based compensation expense	2,065		2,065
Net loss	(24,333)			(24,333)
Ending balance at Mar. 31, 2019	(69,833)	$ 41	343,829	(413,703)
Ending balance, shares at Mar. 31, 2019		41,094,832
Beginning balance at Dec. 31, 2019	$ (48,324)	$ 70	411,255	(459,649)
Beginning balance, shares at Dec. 31, 2019	70,143,252	70,143,252
Issuance of common stock from at the market equity offering	$ 4,178	$ 1	4,177
Issuance of common stock from at the market equity offering, shares		1,230,531
Issuance of common stock upon exercise of stock options, value	$ 60	$ 1	59
Issuance of common stock upon exercise of stock options, shares	110,967	110,967
Issuance of common stock upon vesting of RSUs, net of tax withholdings	$ 120		120
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		110,000
Issuance of common stock under ESPP plan, value	249		249
Issuance of common stock under ESPP plan, shares		76,317
Stock-based compensation expense	1,959		1,959
Unrealized loss on investments	(10)				$ (10)
Net loss	(19,881)			(19,881)
Ending balance at Mar. 31, 2020	$ (61,649)	$ 72	$ 417,819	$ (479,530)	$ (10)
Ending balance, shares at Mar. 31, 2020	71,671,067	71,671,067