Shareholders' Equity - Summary of Changes in Shareholders' Equity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,124,255
Net income	39,058	23,849
Purchase of common stock for treasury	(63,099)
Equity-based compensation	13,399
Tax benefit from equity benefit plan activity	7,998
Proceeds from stock options exercised	43,626
Ending Balance	1,165,237
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	13,399
Tax benefit from equity benefit plan activity	7,998
Proceeds from stock options exercised	43,626
Treasury stock issued upon option exercise and restricted share vesting	(19,755)
Ending Balance	1,370,763
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	4,887,187
Net income	39,058
Ending Balance	4,926,245
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(5,088,633)
Purchase of common stock for treasury	(63,099)
Treasury stock issued upon option exercise and restricted share vesting	19,755
Ending Balance	(5,131,977)
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