CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury stock	Total
Balance at Dec. 31, 2018	$ 3,155	$ 4,238,170	$ 3,914,645	$ (32,864)	$ (4,512,205)	$ 3,610,901
Balance (in shares) at Dec. 31, 2018	630,970				(87,294)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		15,324				15,324
Exercise of stock options	$ 19	35,144				35,163
Exercise of stock options (in shares)	3,871
Unrealized gain, net on available-for-sale securities				120		120
Repurchase of common stock					$ (222,792)	(222,792)
Repurchase of common stock (in shares)					(4,000)
Foreign currency translation				(1,381)		(1,381)
Net income			261,485			261,485
Balance at Mar. 31, 2019	$ 3,174	4,288,638	4,176,130	(34,125)	$ (4,734,997)	3,698,820
Balance (in shares) at Mar. 31, 2019	634,841				(91,294)
Balance at Dec. 31, 2018	$ 3,155	4,238,170	3,914,645	(32,864)	$ (4,512,205)	3,610,901
Balance (in shares) at Dec. 31, 2018	630,970				(87,294)
Increase (Decrease) in Stockholders' Equity
Net income						852,881
Balance at Sep. 30, 2019	$ 3,181	4,370,280	4,767,526	(43,083)	$ (4,989,926)	4,107,978
Balance (in shares) at Sep. 30, 2019	636,235				(95,644)
Balance at Mar. 31, 2019	$ 3,174	4,288,638	4,176,130	(34,125)	$ (4,734,997)	3,698,820
Balance (in shares) at Mar. 31, 2019	634,841				(91,294)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		15,575				15,575
Exercise of stock options	$ 6	45,964				45,970
Exercise of stock options (in shares)	1,288
Unrealized gain, net on available-for-sale securities				215		215
Repurchase of common stock					$ (621)	(621)
Repurchase of common stock (in shares)					(10)
Foreign currency translation				5,154		5,154
Net income			292,473			292,473
Balance at Jun. 30, 2019	$ 3,180	4,350,177	4,468,603	(28,756)	$ (4,735,618)	4,057,586
Balance (in shares) at Jun. 30, 2019	636,129				(91,304)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		15,991				15,991
Exercise of stock options	$ 1	4,112				4,113
Exercise of stock options (in shares)	106
Unrealized gain, net on available-for-sale securities				32		32
Repurchase of common stock					$ (254,308)	(254,308)
Repurchase of common stock (in shares)					(4,340)
Foreign currency translation				(14,359)		(14,359)
Net income			298,923			298,923
Balance at Sep. 30, 2019	$ 3,181	4,370,280	4,767,526	(43,083)	$ (4,989,926)	4,107,978
Balance (in shares) at Sep. 30, 2019	636,235				(95,644)
Balance at Dec. 31, 2019	$ 3,182	4,397,511	5,022,480	(32,387)	$ (5,219,505)	4,171,281
Balance (in shares) at Dec. 31, 2019	636,460				(99,762)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		17,098				17,098
Exercise of stock options	$ 4	13,971				13,975
Exercise of stock options (in shares)	644
Unrealized gain, net on available-for-sale securities				304		304
Repurchase of common stock					$ (579,948)	(579,948)
Repurchase of common stock (in shares)					(10,503)
Foreign currency translation				(30,599)		(30,599)
Net income			278,835			278,835
Balance at Mar. 31, 2020	$ 3,186	4,428,580	5,301,315	(62,682)	$ (5,799,453)	3,870,946
Balance (in shares) at Mar. 31, 2020	637,104				(110,265)
Balance at Dec. 31, 2019	$ 3,182	4,397,511	5,022,480	(32,387)	$ (5,219,505)	$ 4,171,281
Balance (in shares) at Dec. 31, 2019	636,460				(99,762)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)						1,711
Net income						$ 937,858
Balance at Sep. 30, 2020	$ 3,192	4,513,743	5,960,338	(32,529)	$ (5,815,423)	4,629,321
Balance (in shares) at Sep. 30, 2020	638,458				(110,565)
Balance at Mar. 31, 2020	$ 3,186	4,428,580	5,301,315	(62,682)	$ (5,799,453)	3,870,946
Balance (in shares) at Mar. 31, 2020	637,104				(110,265)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		15,936				15,936
Exercise of stock options	$ 4	29,863				29,867
Exercise of stock options (in shares)	820
Unrealized gain, net on available-for-sale securities				200		200
Repurchase of common stock					$ (15,822)	(15,822)
Repurchase of common stock (in shares)					(298)
Foreign currency translation				9,044		9,044
Net income			311,369			311,369
Balance at Jun. 30, 2020	$ 3,190	4,474,379	5,612,684	(53,438)	$ (5,815,275)	4,221,540
Balance (in shares) at Jun. 30, 2020	637,924				(110,563)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		17,668				17,668
Exercise of stock options	$ 2	21,696				21,698
Exercise of stock options (in shares)	534
Unrealized loss, net on available-for-sale securities				(308)		(308)
Repurchase of common stock					$ (148)	(148)
Repurchase of common stock (in shares)					(2)
Foreign currency translation				21,217		21,217
Net income			347,654			347,654
Balance at Sep. 30, 2020	$ 3,192	$ 4,513,743	$ 5,960,338	$ (32,529)	$ (5,815,423)	$ 4,629,321
Balance (in shares) at Sep. 30, 2020	638,458				(110,565)