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, 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]
Unrealized loss on available-for-sale securities, net of tax	721
Net loss	(55,913)
Stockholders' equity ending balance (in shares) at Jun. 30, 2019		52,752,854
Stockholders' equity ending balance at Jun. 30, 2019	$ 499,897	$ 53	1,142,148	(642,464)	160
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in usd per share)	$ 0.001
Stockholders' equity beginning balance (in shares) at Mar. 31, 2019		52,542,518
Stockholders' equity beginning balance at Mar. 31, 2019	$ 510,535	$ 53	1,135,376	(624,602)	(292)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	5,012		5,012
Exercise of stock options (in shares)		64,174
Exercise of stock options	1,760		1,760
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		146,162
Unrealized loss on available-for-sale securities, net of tax	452				452
Net loss	(17,862)			(17,862)
Stockholders' equity ending balance (in shares) at Jun. 30, 2019		52,752,854
Stockholders' equity ending balance at Jun. 30, 2019	$ 499,897	$ 53	1,142,148	(642,464)	160
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in usd per share)	$ 0.001
Common stock, par value (in usd per share)	$ 0.001
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)		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)
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]
Exercise of stock options (in shares)	913,000
Unrealized loss on available-for-sale securities, net of tax	$ (106)
Net loss	(69,391)
Stockholders' equity ending balance (in shares) at Jun. 30, 2020		54,166,712
Stockholders' equity ending balance at Jun. 30, 2020	$ 421,619	$ 54	1,202,445	(780,797)	(83)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in usd per share)	$ 0.001
Stockholders' equity beginning balance (in shares) at Mar. 31, 2020		53,519,920
Stockholders' equity beginning balance at Mar. 31, 2020	$ 413,822	$ 53	1,176,359	(762,346)	(244)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	7,140		7,140
Exercise of stock options (in shares)		617,441
Exercise of stock options	19,610	$ 1	19,609
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		29,351
Vesting of restricted stock units, net of shares withheld for taxes	(663)		(663)
Unrealized loss on available-for-sale securities, net of tax	161				161
Net loss	(18,451)			(18,451)
Stockholders' equity ending balance (in shares) at Jun. 30, 2020		54,166,712
Stockholders' equity ending balance at Jun. 30, 2020	$ 421,619	$ 54	$ 1,202,445	$ (780,797)	$ (83)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, par value (in usd per share)	$ 0.001