Equity-Based Compensation - Summary of SAR 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 Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Outstanding at beginning of year	1,287,724	1,234,787	684,058
Shares, Granted	431,040	387,847	612,681
Shares, Exercised	(102,972)	(95,672)	(31,001)
Shares, Forfeited	(75,978)	(238,965)	(30,678)
Shares, Expired	(4,010)	(273)	(273)
Shares, Outstanding at end of period	1,535,804	1,287,724	1,234,787
Shares, Exercisable at end of period	514,787	305,228	149,318
Weighted-Average Exercise Price, Outstanding at beginning of year	$ 28.91	$ 23.82	$ 19.97
Weighted-Average Exercise Price, Granted	$ 38.51	$ 41.14	$ 27.82
Weighted-Average Exercise Price, Exercised	$ 23.83	$ 22.20	$ 19.56
Weighted-Average Exercise Price, Forfeited	$ 34.10	$ 25.15	$ 22.14
Weighted-Average Exercise Price, Expired	$ 41.57	$ 19.56	$ 19.56
Weighted-Average Exercise Price, Outstanding at end of year	$ 31.66	$ 28.91	$ 23.82
Weighted-Average Exercise Price, Exercisable at end of year	$ 26.52	$ 23.27	$ 20.19
Intrinsic value of exercised options and SARs	$ 1,500,000	$ 1,700,000	$ 353,000