Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Comprehensive Income (Loss)
Stockholders' equity beginning balance (in shares) at Dec. 31, 2018		46,260,747
Stockholders' equity beginning balance at Dec. 31, 2018	$ 292,037	$ 47	$ 879,099	$ (586,549)	$ (560)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	6,992		6,992
Issuance of common stock, net of expense (in shares)		6,151,163
Issuance of common stock, net of expense	248,130	$ 6	248,124
Exercise of stock options (in shares)		35,919
Exercise of stock options	766		766
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		75,028
Vesting of restricted stock units, net of shares withheld for taxes	(393)		(393)
Issuance of common stock related to ESPP (in shares)		19,661
Issuance of common stock related to ESPP	788		788
Unrealized loss on available-for-sale securities, net of tax	268				268
Net loss	(38,053)			(38,053)
Stockholders' equity ending balance (in shares) at Mar. 31, 2019		52,542,518
Stockholders' equity ending balance at Mar. 31, 2019	510,535	$ 53	1,135,376	(624,602)	(292)
Stockholders' equity beginning balance (in shares) at Dec. 31, 2019		53,123,567
Stockholders' equity beginning balance at Dec. 31, 2019	449,476	$ 53	1,160,807	(711,407)	23
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	$ 6,679		6,679
Exercise of stock options (in shares)	296,000	295,757
Exercise of stock options	$ 8,485		8,485
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		77,949
Vesting of restricted stock units, net of shares withheld for taxes	(472)		(472)
Issuance of common stock related to ESPP (in shares)		22,647
Issuance of common stock related to ESPP	860		860
Unrealized loss on available-for-sale securities, net of tax	(267)				(267)
Net loss	(50,939)			(50,939)
Stockholders' equity ending balance (in shares) at Mar. 31, 2020		53,519,920
Stockholders' equity ending balance at Mar. 31, 2020	$ 413,822	$ 53	$ 1,176,359	$ (762,346)	$ (244)