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, 2014		53,826
Beginning balance at Dec. 31, 2014	$ 35,502	$ 5	$ 336,692	$ (301,366)	$ 171
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		565
Issuance of common stock upon the exercise of options	8,448		8,448
Vesting of restricted stock units (in shares)		200
Shares issued under employee stock purchase plan (in shares)		113
Shares issued under employee stock purchase plan	3,035		3,035
Stock-based compensation	45,914		45,914
Net loss	(85,516)			(85,516)
Other comprehensive income (loss), net of tax	439				439
Ending balance (in shares) at Dec. 31, 2015		54,704
Ending balance at Dec. 31, 2015	7,822	$ 5	394,089	(386,882)	610
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		978
Issuance of common stock upon the exercise of options	18,905	$ 1	18,904
Vesting of restricted stock units (in shares)		699
Shares issued under employee stock purchase plan (in shares)		135
Shares issued under employee stock purchase plan	4,286		4,286
Stock-based compensation	58,951		58,951
Net loss	(66,837)			(66,837)
Other comprehensive income (loss), net of tax	3,836				3,836
Ending balance (in shares) at Dec. 31, 2016		56,516
Ending balance at Dec. 31, 2016	$ 26,963	$ 6	476,230	(453,719)	4,446
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)	413	414
Issuance of common stock upon the exercise of options	$ 6,777	$ 0	6,777
Vesting of restricted stock units (in shares)		1,035
Shares issued under employee stock purchase plan (in shares)		182
Shares issued under employee stock purchase plan	$ 5,621		5,621
Repurchase of common stock (in shares)	(635)
Repurchase of common stock	$ (22,599)		(22,599)
Stock-based compensation	70,922		70,922
Net loss	(61,335)			(61,335)
Other comprehensive income (loss), net of tax	(4,229)				(4,229)
Ending balance (in shares) at Dec. 31, 2017		57,512
Ending balance at Dec. 31, 2017	$ 22,120	$ 6	$ 536,951	$ (515,054)	$ 217