Shareholders' Equity - Summary of Changes in Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 1,239,165
Net income	$ 117,392	$ 116,470	274,371	$ 248,923
Purchase of common stock for treasury			(291,743)
Equity-based compensation			32,459
Excess tax benefit from equity benefit plan activity			10,949
Proceeds from stock options exercised			33,938
Ending Balance	1,299,139		1,299,139
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			32,459
Excess tax benefit from equity benefit plan activity			10,949
Proceeds from stock options exercised			33,938
Treasury stock issued upon option exercise and restricted share vesting			(25,371)
Ending Balance	1,499,770		1,499,770
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			5,270,114
Net income			274,371
Ending Balance	5,544,485		5,544,485
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(5,478,950)
Purchase of common stock for treasury			(291,743)
Treasury stock issued upon option exercise and restricted share vesting			25,371
Ending Balance	(5,745,322)		(5,745,322)
Deferred Compensation Trust [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(17,333)
Deferred compensation activity			(34)
Ending Balance	(17,367)		(17,367)
Deferred Compensation Liability [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			17,333
Deferred compensation activity			34
Ending Balance	$ 17,367		$ 17,367