CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive (Loss)/Income
Beginning balance at Dec. 31, 2014	$ 2,217,501	$ 932	$ 904,825	$ 1,539,508	$ (196,010)	$ (31,754)
Beginning balance, shares at Dec. 31, 2014		93,236			2,471
Treasury shares acquired	$ (337,910)				$ (337,910)
Treasury shares acquired, shares	3,833				3,833
Stock-based compensation activity, including tax benefit	$ 79,197		(8,434)		$ 87,631
Stock-based compensation activity, including tax benefit, shares					(1,139)
Other comprehensive (loss)/income	(20,410)					(20,410)
Net income for the year	252,521			252,521
Acquisition-related activity	3,528		(1,922)		$ 5,450
Stockholders' Equity, Other Shares					(68)
Ending balance at Dec. 31, 2015	2,194,427	$ 932	894,469	1,792,029	$ (440,839)	(52,164)
Ending balance, shares at Dec. 31, 2015		93,236			5,097
Treasury shares acquired	$ (336,335)				$ (336,335)
Treasury shares acquired, shares	3,700				3,700
Stock-based compensation activity, including tax benefit	$ 90,165		(11,459)		$ 101,624
Stock-based compensation activity, including tax benefit, shares					(1,249)
Other comprehensive (loss)/income	(5,488)					(5,488)
Net income for the year	265,636			265,636
Ending balance at Dec. 31, 2016	2,208,405	$ 932	883,010	2,057,665	$ (675,550)	(57,652)
Ending balance, shares at Dec. 31, 2016		93,236			7,548
Treasury shares acquired	$ (336,042)				$ (336,042)
Treasury shares acquired, shares	2,750				2,750
Stock-based compensation activity, including tax benefit	$ 94,409		(9,653)		$ 104,062
Stock-based compensation activity, including tax benefit, shares					(1,254)
Other comprehensive (loss)/income	19,808					19,808
Net income for the year	259,251
Ending balance at Dec. 31, 2017	$ 2,245,831	$ 932	$ 873,357	$ 2,316,916	$ (907,530)	$ (37,844)
Ending balance, shares at Dec. 31, 2017		93,236			9,044