CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss), Net	Retained Earnings
Beginning Balance (in shares) at Dec. 31, 2018		79,778
Beginning Balance at Dec. 31, 2018	$ 1,252,891	$ 8	$ 877,514	$ (2,774)	$ 378,143
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	321,514				321,514
Net change in unrealized gains (losses) from investments	317			317
Change in foreign currency translation adjustment, net of tax	530			530
Issuance of common stock relating to employee equity compensation plans (in shares)		529
Issuance of common stock relating to employee equity compensation plans	17,907		17,907
Tax withholdings related to net share settlements of equity awards	(55,793)		(55,793)
Common stock repurchased and retired (shares)		(1,498)
Stock Repurchased and Retired During Period, Value	(299,504)		(15,006)		(284,498)
Stock-based compensation	67,687		67,687
Ending Balance (in shares) at Sep. 30, 2019		78,809
Ending Balance at Sep. 30, 2019	1,305,549	$ 8	892,309	(1,927)	415,159
Beginning Balance (in shares) at Dec. 31, 2018		79,778
Beginning Balance at Dec. 31, 2018	1,252,891	$ 8	877,514	(2,774)	378,143
Ending Balance (in shares) at Dec. 31, 2019		78,433
Ending Balance at Dec. 31, 2019	1,346,169	$ 8	906,937	(688)	439,912
Beginning Balance (in shares) at Jun. 30, 2019		79,865
Beginning Balance at Jun. 30, 2019	1,373,682	$ 8	874,275	(1,876)	501,275
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102,524				102,524
Net change in unrealized gains (losses) from investments	41			41
Change in foreign currency translation adjustment, net of tax	(92)			(92)
Issuance of common stock relating to employee equity compensation plans (in shares)		76
Issuance of common stock relating to employee equity compensation plans	8,293		8,293
Tax withholdings related to net share settlements of equity awards	(3,075)		(3,075)
Common stock repurchased and retired (shares)		(1,132)
Stock Repurchased and Retired During Period, Value	(200,000)		(11,360)		(188,640)
Stock-based compensation	24,176		24,176
Ending Balance (in shares) at Sep. 30, 2019		78,809
Ending Balance at Sep. 30, 2019	1,305,549	$ 8	892,309	(1,927)	415,159
Beginning Balance (in shares) at Dec. 31, 2019		78,433
Beginning Balance at Dec. 31, 2019	1,346,169	$ 8	906,937	(688)	439,912
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,616,900				1,616,900
Net change in unrealized gains (losses) from investments	(194)			(194)
Change in foreign currency translation adjustment, net of tax	25,793			25,793
Issuance of common stock relating to employee equity compensation plans (in shares)		416
Issuance of common stock relating to employee equity compensation plans	20,314		20,314
Tax withholdings related to net share settlements of equity awards	(48,674)		(48,674)
Stock-based compensation	73,163		73,163
Ending Balance (in shares) at Sep. 30, 2020		78,849
Ending Balance at Sep. 30, 2020	3,033,471	$ 8	951,740	24,911	2,056,812
Beginning Balance (in shares) at Jun. 30, 2020		78,781
Beginning Balance at Jun. 30, 2020	2,845,045	$ 8	918,495	9,101	1,917,441
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	139,371				139,371
Change in foreign currency translation adjustment, net of tax	15,810			15,810
Issuance of common stock relating to employee equity compensation plans (in shares)		68
Issuance of common stock relating to employee equity compensation plans	9,652		9,652
Tax withholdings related to net share settlements of equity awards	(1,636)		(1,636)
Stock-based compensation	25,229		25,229
Ending Balance (in shares) at Sep. 30, 2020		78,849
Ending Balance at Sep. 30, 2020	$ 3,033,471	$ 8	$ 951,740	$ 24,911	$ 2,056,812