Shareholders' Equity - Summary of Changes in Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 1,239,165
Net income	$ 91,676	$ 93,395	156,979	$ 132,453
Purchase of common stock for treasury			(96,508)
Equity-based compensation			21,378
Excess tax benefit from equity benefit plan activity			8,678
Proceeds from stock options exercised			27,909
Ending Balance	1,357,601		1,357,601
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			206
Ending Balance	206		206
Additional Paid-In-Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			1,447,795
Equity-based compensation			21,378
Excess tax benefit from equity benefit plan activity			8,678
Proceeds from stock options exercised			27,909
Treasury stock issued upon option exercise and restricted share vesting			(22,696)
Ending Balance	1,483,064		1,483,064
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			5,270,114
Net income			156,979
Ending Balance	5,427,093		5,427,093
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(5,478,950)
Purchase of common stock for treasury			(96,508)
Treasury stock issued upon option exercise and restricted share vesting			22,696
Ending Balance	(5,552,762)		(5,552,762)
Deferred Compensation Trust [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(17,333)
Deferred compensation activity			(22)
Ending Balance	(17,355)		(17,355)
Deferred Compensation Liability [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			17,333
Deferred compensation activity			22
Ending Balance	$ 17,355		$ 17,355