CONDENSED 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
Cumulative effect of the ASC 606 adoption	$ 183,132			$ 183,132
Beginning balance at Dec. 31, 2017	$ 2,245,831	$ 932	$ 873,357	2,316,916	$ (907,530)	$ (37,844)
Beginning balance, shares at Dec. 31, 2017		93,236			9,044
Treasury shares acquired	750				750
Treasury shares acquired, amount	$ (117,831)				$ (117,831)
Stock-based compensation activity	3,705		(39,943)		$ 43,648
Stock-based compensation activity, shares					(492)
Other comprehensive (loss)/income	8,243					8,243
Net income	84,280			84,280
Ending balance at Mar. 31, 2018	2,407,360	$ 932	833,414	2,584,328	$ (981,713)	(29,601)
Ending balance, shares at Mar. 31, 2018		93,236			9,302
Beginning balance at Dec. 31, 2018	$ 2,649,547	$ 932	867,462	2,919,411	$ (1,075,879)	(62,379)
Beginning balance, shares at Dec. 31, 2018		93,236			9,602
Treasury shares acquired	250				250
Treasury shares acquired, amount	$ (44,856)				$ (44,856)
Stock-based compensation activity	1,018		(42,465)		$ 43,483
Stock-based compensation activity, shares					(494)
Other comprehensive (loss)/income	(7,558)					(7,558)
Net income	86,230			86,230
Ending balance at Mar. 31, 2019	$ 2,684,381	$ 932	$ 824,997	$ 3,005,641	$ (1,077,252)	$ (69,937)
Ending balance, shares at Mar. 31, 2019		93,236			9,358