Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total		Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-09	$ 11,423				$ 11,423
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2014-09	118,225				118,117	$ 108
Beginning balance (in shares) at Dec. 31, 2015			160,785,764
Beginning balance at Dec. 31, 2015	566,814		$ 160	$ 1,140,545	(557,009)	(16,882)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee stock plans (in shares)			6,645,009
Common stock issued under employee stock plans	66,368		$ 7	66,361
Taxes paid related to net share settlement of equity awards	(119,914)			(119,914)
Stock-based compensation	318,325			318,325
Other comprehensive loss, net	(5,899)	[1]				(5,899)
Net loss	(414,249)	[1],[2]			(414,249)
Ending balance (in shares) at Dec. 31, 2016			167,430,773
Ending balance at Dec. 31, 2016	541,093		$ 167	1,405,317	(841,718)	(22,673)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee stock plans (in shares)			7,385,897
Common stock issued under employee stock plans	82,559		$ 7	82,552
Repurchases and retirement of common stock (in shares)			(540,806)
Repurchases and retirement of common stock	(55,000)			(55,000)
Taxes paid related to net share settlement of equity awards	(182,127)			(182,127)
Stock-based compensation	394,680			394,680
Equity component of the convertible notes, net	159,891			159,891
Purchase of convertible note hedge	(128,017)			(128,017)
Issuance of warrants	54,071			54,071
Other comprehensive loss, net	28,440	[1]				28,440
Net loss	(116,846)	[1],[2]			(116,846)
Ending balance (in shares) at Dec. 31, 2017			174,275,864
Ending balance at Dec. 31, 2017	778,744	[3]	$ 174	1,731,367	(958,564)	5,767
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-01	0				7,234	(7,234)
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-16	(746)				(746)
Common stock issued under employee stock plans (in shares)			5,899,519
Common stock issued under employee stock plans	104,173		$ 6	104,167
Taxes paid related to net share settlement of equity awards	(281,061)			(281,061)
Stock-based compensation	545,805			545,805
Settlement of 2018 Notes conversion feature (in shares)			1,313,589
Settlement of 2018 Notes conversion feature	(773,301)		$ 1	(773,302)
Benefit from exercise of 2018 Note Hedges (in shares)			(1,313,617)
Benefit from exercise of 2018 Note Hedges	766,857		$ (1)	766,858
Other comprehensive loss, net	(2,568)					(2,568)
Net loss	(26,704)				(26,704)
Ending balance (in shares) at Dec. 31, 2018			180,175,355
Ending balance at Dec. 31, 2018	$ 1,111,199		$ 180	$ 2,093,834	(978,780)	$ (4,035)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-01					$ 7,200

[1] As adjusted to reflect the impact of the full retrospective adoption of Topic 606.

[2] As adjusted to reflect the impact of the full retrospective adoption of Topic 606.

[3] As adjusted to reflect the impact of the full retrospective adoption of Topic 606.