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, 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)
Increase (Decrease) in Stockholders' Equity
Stock-based compensation		13,439				13,439
Exercise of stock options	$ 4	6,498				6,502
Exercise of stock options (in shares)	669
Unrealized gain on available-for- sale securities				215		215
ASU No. 2016-16 adoption | ASU 2016-16			(6,585)			(6,585)
Repurchase of common stock					$ (251,949)	(251,949)
Repurchase of common stock (in shares)					(4,362)
Foreign currency translation				2,723		2,723
Net income			216,050			216,050
Balance at Mar. 31, 2018	$ 3,150	4,170,565	3,137,691	(13,721)	$ (3,422,078)	3,875,607
Balance (in shares) at Mar. 31, 2018	629,924				(67,319)
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 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)