Shareholders' Equity - Summary of Changes in Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 1,124,255
Net income	$ 116,470	$ 90,152	248,923	$ 182,179
Purchase of common stock for treasury			(263,446)
Equity-based compensation			39,874
Tax benefit from equity benefit plan activity			14,465
Proceeds from stock options exercised			76,419
Ending Balance	1,240,490		1,240,490
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			1,325,495
Equity-based compensation			39,874
Tax benefit from equity benefit plan activity			14,465
Proceeds from stock options exercised			76,419
Treasury stock issued upon option exercise and restricted share vesting			(36,039)
Ending Balance	1,420,214		1,420,214
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			4,887,187
Net income			248,923
Ending Balance	5,136,110		5,136,110
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(5,088,633)
Purchase of common stock for treasury			(263,446)
Treasury stock issued upon option exercise and restricted share vesting			36,039
Ending Balance	(5,316,040)		(5,316,040)
Deferred Compensation Trust [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(17,333)
Ending Balance	(17,333)		(17,333)
Deferred Compensation Liability [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			17,333
Ending Balance	$ 17,333		$ 17,333