Shareholders' Equity - Summary of Changes in Shareholders' Equity (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,239,165
Net income	65,303	$ 39,058
Purchase of common stock for treasury	(87,101)
Equity-based compensation	10,549
Excess tax benefit from equity benefit plan activity	6,284
Proceeds from stock options exercised	22,263
Ending Balance	1,256,463
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	206
Ending Balance	206
Additional Paid-In-Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	1,447,795
Equity-based compensation	10,549
Excess tax benefit from equity benefit plan activity	6,284
Proceeds from stock options exercised	22,263
Treasury stock issued upon option exercise and restricted share vesting	(19,891)
Ending Balance	1,467,000
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	5,270,114
Net income	65,303
Ending Balance	5,335,417
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(5,478,950)
Purchase of common stock for treasury	(87,101)
Treasury stock issued upon option exercise and restricted share vesting	19,891
Ending Balance	(5,546,160)
Deferred Compensation Trust [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(17,333)
Deferred compensation activity	(10)
Ending Balance	(17,343)
Deferred Compensation Liability [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	17,333
Deferred compensation activity	10
Ending Balance	$ 17,343