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, 2014	$ 3,105	$ 424,075	$ 2,330,510	$ (11,453)	$ (1,231,087)	$ 1,515,150
Balance (in shares) at Dec. 31, 2014	621,012				(117,846)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		32,719				32,719
Exercise of stock options	$ 111	49,217				49,328
Exercise of stock options (in shares)	22,275
Issuance of Common Stock	$ 511	3,168,624				3,169,135
Issuance of common stock (in shares)	102,123
Excess tax benefits from share based payment arrangements		314,737				314,737
Repurchase of common stock					$ (807,967)	(807,967)
Repurchase of common stock (in shares)					(18,864)
Cancellation of treasury stock	$ (622)	415	(1,482,380)		$ 1,482,587
Cancellation of treasury stock (in shares)	(124,353)				124,353
Foreign currency translation				(10,425)		(10,425)
Net income			546,733			546,733
Balance at Dec. 31, 2015	$ 3,105	3,989,787	1,394,863	(21,878)	$ (556,467)	4,809,410
Balance (in shares) at Dec. 31, 2015	621,057				(12,357)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		45,848				45,848
Exercise of stock options	$ 11	16,441				16,452
Exercise of stock options (in shares)	2,144
Unrealized loss on available-for-sale securities				(193)		(193)
Excess tax deficiency from share based payment arrangements		(831)				(831)
Repurchase of common stock					$ (2,252,484)	(2,252,484)
Repurchase of common stock (in shares)					(44,278)
Foreign currency translation				(1,178)		(1,178)
Net income			712,685			712,685
Balance at Dec. 31, 2016	$ 3,116	4,051,245	2,107,548	(23,249)	$ (2,808,951)	3,329,709
Balance (in shares) at Dec. 31, 2016	623,201				(56,635)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		52,282				52,282
Exercise of stock options	$ 30	52,596				52,626
Exercise of stock options (in shares)	6,054
Unrealized loss on available-for-sale securities				(648)		(648)
Excess tax deficiency from share based payment arrangements		(5,495)				(5,495)
Repurchase of common stock					$ (361,178)	(361,178)
Repurchase of common stock (in shares)					(6,322)
Foreign currency translation				7,238		7,238
Net income			820,678			820,678
Balance at Dec. 31, 2017	$ 3,146	$ 4,150,628	$ 2,928,226	$ (16,659)	$ (3,170,129)	$ 3,895,212
Balance (in shares) at Dec. 31, 2017	629,255				(62,957)