Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Comprehensive (Loss) Income
Stockholders' equity beginning balance (in shares) at Dec. 31, 2016		38,251,826
Stockholders' equity beginning balance at Dec. 31, 2016	$ 225,597	$ 39	$ 590,474	$ (364,491)	$ (425)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stock-based compensation	28,248		28,248
Issuance of common stock (in shares)		6,216,216
Issuance of common stock	215,802	$ 6	215,796
Exercise of stock options (in shares)		474,056
Exercise of stock options	3,893	$ 1	3,892
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		282,158
Vesting of restricted stock units, net of shares withheld for taxes	(226)		(226)
Issuance of common stock related to ESPP (in shares)		33,698
Issuance of common stock related to ESPP	827		827
Net exercise of warrants to purchase common stock (in shares)		3,221
Net exercise of warrants to purchase common stock	0
Unrealized gain/loss on available-for-sale securities, net of tax	(470)				(470)
Net loss	(108,454)			(108,454)
Stockholders' equity ending balance (in shares) at Dec. 31, 2017		45,261,175
Stockholders' equity ending balance at Dec. 31, 2017	365,217	$ 46	839,090	(473,024)	(895)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stock-based compensation	24,569		24,569
Exercise of stock options (in shares)		779,711
Exercise of stock options	15,931	$ 1	15,930
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		170,516
Vesting of restricted stock units, net of shares withheld for taxes	(731)		(731)
Issuance of common stock related to ESPP (in shares)		30,896
Issuance of common stock related to ESPP	1,085		1,085
Net exercise of warrants to purchase common stock (in shares)		18,449
Net exercise of warrants to purchase common stock	797		797
Unrealized gain/loss on available-for-sale securities, net of tax	335				335
Net loss	(118,871)			(118,871)
Stockholders' equity ending balance (in shares) at Dec. 31, 2018		46,260,747
Stockholders' equity ending balance at Dec. 31, 2018	292,037	$ 47	879,099	(586,549)	(560)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stock-based compensation	22,995		22,995
Issuance of common stock (in shares)		6,151,163
Issuance of common stock	$ 248,130	$ 6	248,124
Exercise of stock options (in shares)	344,000	344,257
Exercise of stock options	$ 10,096		10,096
Vesting of restricted stock units, net of shares withheld for taxes (in shares)		334,141
Vesting of restricted stock units, net of shares withheld for taxes	(802)		(802)
Issuance of common stock related to ESPP (in shares)		33,259
Issuance of common stock related to ESPP	1,295		1,295
Unrealized gain/loss on available-for-sale securities, net of tax	583				583
Net loss	(124,858)			(124,858)
Stockholders' equity ending balance (in shares) at Dec. 31, 2019		53,123,567
Stockholders' equity ending balance at Dec. 31, 2019	$ 449,476	$ 53	$ 1,160,807	$ (711,407)	$ 23