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
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	(117,831)				$ (117,831)
Treasury shares acquired, shares					750
Stock-based compensation activity			(39,943)
Stock-based compensation activity	3,705				$ 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, 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	$ (192,787)
Treasury shares acquired, shares	1,174
Net income	$ 266,212
Ending balance at Sep. 30, 2018	2,548,546	$ 932	850,616	2,766,259	$ (1,008,370)	(60,891)
Ending balance, shares at Sep. 30, 2018		93,236			9,214
Beginning balance at Mar. 31, 2018	2,407,360	$ 932	833,414	2,584,328	$ (981,713)	(29,601)
Beginning balance, shares at Mar. 31, 2018		93,236			9,302
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation activity			3,910
Stock-based compensation activity	33,711				$ 29,801
Stock-based compensation activity, shares					(313)
Other comprehensive (loss)/income	(26,188)					(26,188)
Net income	92,596			92,596
Ending balance at Jun. 30, 2018	2,507,479	$ 932	837,324	2,676,924	$ (951,912)	(55,789)
Ending balance, shares at Jun. 30, 2018		93,236			8,989
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	(74,956)				$ (74,956)
Treasury shares acquired, shares					424
Stock-based compensation activity			13,292
Stock-based compensation activity	31,790				$ 18,498
Stock-based compensation activity, shares					(199)
Other comprehensive (loss)/income	(5,102)					(5,102)
Net income	89,336			89,336
Ending balance at Sep. 30, 2018	2,548,546	$ 932	850,616	2,766,259	$ (1,008,370)	(60,891)
Ending balance, shares at Sep. 30, 2018		93,236			9,214
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	(44,856)				$ (44,856)
Treasury shares acquired, shares					250
Stock-based compensation activity			(42,465)
Stock-based compensation activity	1,018				$ 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
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	$ (59,116)
Treasury shares acquired, shares	330
Net income	$ 285,443
Ending balance at Sep. 30, 2019	2,923,324	$ 932	865,634	3,204,854	$ (1,057,955)	(90,141)
Ending balance, shares at Sep. 30, 2019		93,236			9,072
Beginning balance at Mar. 31, 2019	2,684,381	$ 932	824,997	3,005,641	$ (1,077,252)	(69,937)
Beginning balance, shares at Mar. 31, 2019		93,236			9,358
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	(14,260)				$ (14,260)
Treasury shares acquired, shares					80
Stock-based compensation activity			14,699
Stock-based compensation activity	36,857				$ 22,158
Stock-based compensation activity, shares					(241)
Other comprehensive (loss)/income	558					558
Net income	109,750			109,750
Ending balance at Jun. 30, 2019	2,817,286	$ 932	839,696	3,115,391	$ (1,069,354)	(69,379)
Ending balance, shares at Jun. 30, 2019		93,236			9,197
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation activity			25,938
Stock-based compensation activity	37,337				$ 11,399
Stock-based compensation activity, shares					(125)
Other comprehensive (loss)/income	(20,762)					(20,762)
Net income	89,463			89,463
Ending balance at Sep. 30, 2019	$ 2,923,324	$ 932	$ 865,634	$ 3,204,854	$ (1,057,955)	$ (90,141)
Ending balance, shares at Sep. 30, 2019		93,236			9,072