Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Balance at (in shares) at Dec. 31, 2017			25,421,000
Balances at at Dec. 31, 2017	$ 40,109	$ (754)	$ 2	$ 353,308	$ (99)	$ (313,102)	$ (754)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock net of issuance costs (in shares)			4,600,000
Issuance of common stock net of issuance costs	53,829		$ 1	53,828
Issuance of common stock warrants	4,593			4,593
Exercise of stock options (in shares)			517,000
Common stock issued for stock options and restricted stock units	3,507			3,507
Issuance of common stock for employee stock purchase plan (in shares)			257,000
Issuance of common stock for employee stock purchase plan	1,451			1,451
Exercise of common stock warrant, net (in shares)			118,000
Exercise of common stock warrants	0
Stock-based compensation	11,475			11,475
Net loss	(77,400)					(77,400)
Other comprehensive income	59				59
Balance at (in shares) at Dec. 31, 2018			30,913,000
Balances at at Dec. 31, 2018	36,869		$ 3	428,162	(40)	(391,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock net of issuance costs (in shares)			3,175,000
Issuance of common stock net of issuance costs	68,273			68,273
Issuance of common stock warrants	3,197		$ 1	3,196
Exercise of stock options (in shares)			2,007,000
Common stock issued for stock options and restricted stock units	18,387			18,387
Issuance of common stock for employee stock purchase plan (in shares)			203,000
Issuance of common stock for employee stock purchase plan	1,952			1,952
Tax withholdings related to net share settlements of restricted stock units	(1,474)			(1,474)
Stock-based compensation	17,458			17,458
Net loss	(40,696)					(40,696)
Other comprehensive income	185				185
Balance at (in shares) at Dec. 31, 2019			36,298,000
Balances at at Dec. 31, 2019	104,151		$ 4	535,954	145	(431,952)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock net of issuance costs (in shares)			5,750,000
Issuance of common stock net of issuance costs	215,765			215,765
Issuance of common stock warrants	$ 737			737
Exercise of stock options (in shares)	1,483,602		1,890,000
Common stock issued for stock options and restricted stock units	$ 18,751			18,751
Issuance of common stock for employee stock purchase plan (in shares)			89,000
Issuance of common stock for employee stock purchase plan	2,190			2,190
Exercise of common stock warrant, net (in shares)			414,000
Exercise of common stock warrants	0
Tax withholdings related to net share settlements of restricted stock units	(2,012)			(2,012)
Stock-based compensation	18,963			18,963
Net loss	(110,078)					(110,078)
Other comprehensive income	(62)				(62)
Balance at (in shares) at Dec. 31, 2020			44,441,000
Balances at at Dec. 31, 2020	$ 306,948		$ 4	$ 848,891	$ 83	$ (542,030)