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, 2013		52,470
Beginning balance at Dec. 31, 2013	$ 52,895	$ 5	$ 289,307	$ (236,467)	$ 50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)		1,154
Issuance of common stock upon the exercise of options	12,142		12,142
Vesting of restricted stock units (in shares)		202
Stock-based compensation	35,243		35,243
Net loss	(64,899)			(64,899)
Other comprehensive income, net of tax	121				121
Ending balance at Dec. 31, 2014	35,502	$ 5	336,692	(301,366)	171
Ending balance (in shares) at Dec. 31, 2014		53,826
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, net of tax	439				439
Ending balance at Dec. 31, 2015	$ 7,822	$ 5	394,089	(386,882)	610
Ending balance (in shares) at Dec. 31, 2015		54,704
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of options (in shares)	978	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, net of tax	3,836				3,836
Ending balance at Dec. 31, 2016	$ 26,963	$ 6	$ 476,230	$ (453,719)	$ 4,446
Ending balance (in shares) at Dec. 31, 2016		56,516