Equity-Based Compensation - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Granted
Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at beginning of year	1,702,650	2,340,959	2,767,887
Shares, Granted	0	0	0
Shares, Exercised	(148,802)	(490,715)	(273,564)
Shares, Forfeited	(1,663)	(63,714)	(62,798)
Shares, Expired	(20,341)	(83,880)	(90,566)
Shares, Outstanding at end of period	1,531,844	1,702,650	2,340,959
Shares, Exercisable at end of period	1,527,814	1,589,096	1,893,346
Weighted-Average Exercise Price, Outstanding at beginning of year	$ 40.43	$ 37.35	$ 35.98
Weighted-Average Exercise Price, Granted	$ 0	$ 0	$ 0
Weighted-Average Exercise Price, Exercised	$ 27.02	$ 26.63	$ 23.43
Weighted-Average Exercise Price, Forfeited	$ 36.36	$ 32.29	$ 35.87
Weighted-Average Exercise Price, Expired	$ 43.63	$ 40.76	$ 35.08
Weighted-Average Exercise Price, Outstanding at end of year	$ 41.69	$ 40.43	$ 37.35
Weighted-Average Exercise Price, Exercisable at end of year	$ 41.75	$ 40.84	$ 37.50
Intrinsic value of exercised options and SARs	$ 1,700,000	$ 6,400,000	$ 2,214,000