Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Retained Earnings (Accumulated Deficit)	Retained Earnings (Accumulated Deficit) Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Dec. 31, 2017			169,893,324
Beginning Balance at Dec. 31, 2017	$ 3,362,469	$ (38,601)	$ 1,699	$ 4,073,362	$ 0	$ (21,930)	$ (690,662)	$ (38,601)
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)			2,235,212
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 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	$ 851	$ 1,629	3,670,033	0	(48,912)	(430,890)	$ 851
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)			2,251,840
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	(72,328)		$ 22	(72,350)
Issuance of common stock under employee stock purchase plan (in shares)			879,648
Issuance of common stock under employee stock purchase plan	53,689		$ 9	53,680
Stock-based compensation	222,857			222,857
Equity component of convertible senior notes, net of deferred tax of $4,971 and issuance costs of $4,418	240,820			240,820
Issuance of warrants related to convertible senior notes	185,150			185,150
Purchase of note hedge related to convertible senior notes	(312,225)			(312,225)
Repurchases of common stock (in shares)			(4,035,195)
Repurchases of common stock	(334,519)				(334,519)
Treasury stock retirement	0		$ (40)	(334,479)	334,519
Net income	478,035						478,035
Foreign currency translation adjustments	(1,020)					(1,020)
Change in unrealized gain on investments, net of tax	4,788					4,788
Ending balance (in shares) at Dec. 31, 2019			162,000,843
Ending Balance at Dec. 31, 2019	3,657,958		$ 1,620	3,653,486	0	(45,144)	47,996
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)			1,949,963
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	(89,102)		$ 20	(89,122)
Issuance of common stock under employee stock purchase plan (in shares)			723,600
Issuance of common stock under employee stock purchase plan	58,402		$ 7	58,395
Stock-based compensation	235,629			235,629
Repurchases of common stock (in shares)			(1,964,686)
Repurchases of common stock	(193,588)				(193,588)
Treasury stock retirement	0		$ (20)	(193,568)	193,588
Net income	557,054						557,054
Foreign currency translation adjustments	19,629					19,629
Change in unrealized gain on investments, net of tax	5,314					5,314
Ending balance (in shares) at Dec. 31, 2020			162,709,720
Ending Balance at Dec. 31, 2020	$ 4,251,296		$ 1,627	$ 3,664,820	$ 0	$ (20,201)	$ 605,050