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, 2014		178,300,603
Beginning Balance at Dec. 31, 2014	$ 2,945,335	$ 1,783	$ 4,559,430	$ 0	$ (17,611)	$ (1,598,267)
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)		2,756,357
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	(27,670)	$ 27	(27,697)
Issuance of common stock under employee stock purchase plan (in shares)		668,654
Issuance of common stock under employee stock purchase plan	34,841	$ 7	34,834
Stock-based compensation	144,544		144,544
Tax benefit (deficiency) from stock-based award activity, net	28,870		28,870
Repurchases of common stock (in shares)		(4,513,433)
Repurchases of common stock	(302,606)			(302,606)
Treasury stock retirement	0	$ (45)	(302,561)	302,606
Net income	321,406					321,406
Foreign currency translation adjustments	(22,872)				(22,872)
Change in unrealized gain on investments, net of tax	(970)				(970)
Ending balance (in shares) at Dec. 31, 2015		177,212,181
Ending Balance at Dec. 31, 2015	3,120,878	$ 1,772	4,437,420	0	(41,453)	(1,276,861)
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	316,132					316,132
Foreign currency translation adjustments	(14,081)				(14,081)
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	3,224,370	$ 1,733	4,239,588	0	(56,222)	(960,729)
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	218,321					218,321
Foreign currency translation adjustments	34,698				34,698
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	$ 3,310,723	$ 1,699	$ 4,073,362	$ 0	$ (21,930)	$ (742,408)