Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital (Deficit)	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		57,512
Beginning balance at Dec. 31, 2017	$ 22,120	$ 6	$ 536,951	$ (515,054)	$ 217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		835
Issuance of common stock upon the exercise of options	26,981		26,981
Vesting of restricted stock units (in shares)		662
Vesting of restricted stock units	0
Shares issued under employee stock purchase plan (in shares)		102
Shares issued under employee stock purchase plan	3,080		3,080
Repurchase of common stock (in shares)		(867)
Repurchase of common stock	(36,743)		(36,743)
Stock-based compensation	37,962		37,962
Net loss	(28,223)			(28,223)
Other comprehensive loss, net of tax	60				60
Ending balance (in shares) at Jun. 30, 2018		58,244
Ending balance at Jun. 30, 2018	44,172	$ 6	568,231	(524,342)	277
Beginning balance (in shares) at Mar. 31, 2018		57,525
Beginning balance at Mar. 31, 2018	32,361	$ 6	546,808	(512,335)	(2,118)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		624
Issuance of common stock upon the exercise of options	21,832		21,832
Vesting of restricted stock units (in shares)		437
Vesting of restricted stock units	0
Shares issued under employee stock purchase plan (in shares)		102
Shares issued under employee stock purchase plan	3,080		3,080
Repurchase of common stock (in shares)		(444)
Repurchase of common stock	(20,719)		(20,719)
Stock-based compensation	17,230		17,230
Net loss	(12,007)			(12,007)
Other comprehensive loss, net of tax	2,395				2,395
Ending balance (in shares) at Jun. 30, 2018		58,244
Ending balance at Jun. 30, 2018	44,172	$ 6	568,231	(524,342)	277
Beginning balance (in shares) at Dec. 31, 2018		58,886
Beginning balance at Dec. 31, 2018	$ 55,907	$ 6	585,387	(529,962)	476
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)	270	270
Issuance of common stock upon the exercise of options	$ 10,147		10,147
Vesting of restricted stock units (in shares)		731
Vesting of restricted stock units	0
Shares issued under employee stock purchase plan (in shares)		90
Shares issued under employee stock purchase plan	3,927		3,927
Stock-based compensation	38,309		38,309
Net loss	(12,269)			(12,269)
Other comprehensive loss, net of tax	1,376				1,376
Ending balance (in shares) at Jun. 30, 2019		59,977
Ending balance at Jun. 30, 2019	97,397	$ 6	637,770	(542,231)	1,852
Beginning balance (in shares) at Mar. 31, 2019		59,407
Beginning balance at Mar. 31, 2019	75,565	$ 6	608,168	(533,426)	817
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		141
Issuance of common stock upon the exercise of options	5,163		5,163
Vesting of restricted stock units (in shares)		339
Vesting of restricted stock units	0
Shares issued under employee stock purchase plan (in shares)		90
Shares issued under employee stock purchase plan	3,927		3,927
Stock-based compensation	20,512		20,512
Net loss	(8,805)			(8,805)
Other comprehensive loss, net of tax	1,035				1,035
Ending balance (in shares) at Jun. 30, 2019		59,977
Ending balance at Jun. 30, 2019	$ 97,397	$ 6	$ 637,770	$ (542,231)	$ 1,852