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 (Loss) [Member]
Beginning balance at Dec. 31, 2019	$ (48,324)	$ 70	$ 411,255	$ (459,649)
Beginning balance, shares at Dec. 31, 2019		70,143,252
Issuance of common stock from at the market equity offering, value	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
Issuance of common stock upon vesting of RSUs, net of tax withholdings, value	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 gain (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
Beginning balance at Dec. 31, 2020	$ 174,750	$ 91	723,482	(548,776)	(47)
Beginning balance, shares at Dec. 31, 2020	91,459,239	91,459,239
Issuance of common stock upon exercise of stock options, value	$ 372	$ 1	371
Issuance of common stock upon exercise of stock options, shares	104,184	104,184
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		650
Issuance of common stock under ESPP plan, value	$ 392		392
Issuance of common stock under ESPP plan, shares		24,191
Stock-based compensation expense	3,624		3,624
Unrealized gain (loss) on investments	32				32
Net loss	(35,465)			(35,465)
Ending balance at Mar. 31, 2021	$ 143,705	$ 92	$ 727,869	$ (584,241)	$ (15)
Ending balance, shares at Mar. 31, 2021	91,588,264	91,588,264