Shareholders' Equity - Summary of Changes in Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 1,124,255
Net income	$ 93,395	$ 68,178	132,453	$ 92,027
Purchase of common stock for treasury			(69,285)
Equity-based compensation			26,303
Tax benefit from equity benefit plan activity			9,899
Proceeds from stock options exercised			51,256
Ending Balance	1,274,881		1,274,881
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			26,303
Tax benefit from equity benefit plan activity			9,899
Proceeds from stock options exercised			51,256
Treasury stock issued upon option exercise and restricted share vesting			(23,228)
Ending Balance	1,389,725		1,389,725
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			4,887,187
Net income			132,453
Ending Balance	5,019,640		5,019,640
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			(5,088,633)
Purchase of common stock for treasury			(69,285)
Treasury stock issued upon option exercise and restricted share vesting			23,228
Ending Balance	(5,134,690)		(5,134,690)
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