Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2015		177,212,181
Beginning Balance at Dec. 31, 2015	$ 3,162,865	$ 1,772	$ 4,437,420	$ 0	$ (42,172)	$ (1,234,155)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of stock options and vesting of restricted and deferred stock units, net of shares withheld for employee taxes (in shares)		2,194,699
Issuance of common stock upon the exercise of stock options and vesting of restricted and deferred stock units, net of shares withheld for employee taxes	(27,394)	$ 22	(27,416)
Issuance of common stock under employee stock purchase plan (in shares)		863,419
Issuance of common stock under employee stock purchase plan	39,914	$ 9	39,905
Stock-based compensation	166,987		166,987
Tax benefit (deficiency) from stock-based award activity, net	(3,584)		(3,584)
Repurchases of common stock (in shares)		(7,015,502)
Repurchases of common stock	(373,794)			(373,794)
Treasury stock retirement	0	$ (70)	(373,724)	373,794
Net income	320,727					320,727
Foreign currency translation adjustments	(14,815)				(14,815)
Change in unrealized gain on investments, net of tax	(688)				(688)
Ending balance (in shares) at Dec. 31, 2016		173,254,797
Ending Balance at Dec. 31, 2016	3,270,218	$ 1,733	4,239,588	0	(57,675)	(913,428)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the exercise of stock options and vesting of restricted and deferred stock units, net of shares withheld for employee taxes (in shares)		2,453,961
Issuance of common stock upon the exercise of stock options and vesting of restricted and deferred stock units, net of shares withheld for employee taxes	(40,538)	$ 24	(40,562)
Issuance of common stock under employee stock purchase plan (in shares)		1,052,684
Issuance of common stock under employee stock purchase plan	42,302	$ 11	42,291
Stock-based compensation	193,170		193,170
Repurchases of common stock (in shares)		(6,868,118)
Repurchases of common stock	(361,194)			(361,194)
Treasury stock retirement	0	$ (69)	(361,125)	361,194
Net income	222,766					222,766
Foreign currency translation adjustments	36,151				36,151
Change in unrealized gain on investments, net of tax	(406)				(406)
Ending balance (in shares) at Dec. 31, 2017		169,893,324
Ending Balance at Dec. 31, 2017	3,362,469	$ 1,699	4,073,362	0	(21,930)	(690,662)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment to accumulated deficit related to adoption of new accounting pronouncement	(38,601)					(38,601)
Issuance of common stock upon the exercise of stock options and vesting of restricted and deferred stock units, net of shares withheld for employee taxes (in shares)		2,235,212
Issuance of common stock upon the exercise of stock options and vesting of restricted and deferred stock units, net of shares withheld for employee taxes	(56,544)	$ 22	(56,566)
Issuance of common stock under employee stock purchase plan (in shares)		973,975
Issuance of common stock under employee stock purchase plan	50,688	$ 10	50,678
Stock-based compensation	218,416		218,416
Equity component of convertible senior notes, net of deferred tax of $4,971 and issuance costs of $4,418	275,836		275,836
Issuance costs of convertible senior notes	4,418
Deferred tax of convertible senior notes	4,971
Issuance of warrants related to convertible senior notes	119,945		119,945
Purchase of note hedge related to convertible senior notes	(261,740)		(261,740)
Repurchases of common stock (in shares)		(10,197,961)
Repurchases of common stock	(750,000)			(750,000)
Treasury stock retirement	0	$ (102)	(749,898)	750,000
Net income	298,373					298,373
Foreign currency translation adjustments	(27,585)				(27,585)
Change in unrealized gain on investments, net of tax	603				603
Ending balance (in shares) at Dec. 31, 2018		162,904,550
Ending Balance at Dec. 31, 2018	$ 3,191,860	$ 1,629	$ 3,670,033	$ 0	$ (48,912)	$ (430,890)