Stock-Based Compensation (Detail) - Summary Of Changes In SARs Outstanding (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Granted	1 year 73 days
Stock Appreciation Rights (SARs) [Member] | Unvested [Member]
Outstanding (in Shares)	1,200,000
Stock Appreciation Rights (SARs) [Member]
Outstanding (in Shares)	2,100,000	[1],[2]	2,500,000
Per Share Weighted- Average Exercise Price	$ 24.27	[1],[2]	$ 20.39
Per Share Weighted- Average Grant Date Fair Value	$ 8.94	[1],[2]	$ 7.66
Weighted Average Remaining Contractual Term	4 years 83 days	[1],[2]	4 years
Vested and exercisable at September 30, 2012 (2) (in Shares)	900,000	[2]
Vested and exercisable at September 30, 2012 (2)	$ 18.50	[2]
Vested and exercisable at September 30, 2012 (2)	$ 7.08	[2]
Vested and exercisable at September 30, 2012 (2)	3 years 62 days	[2]
Granted (in Shares)	400,000
Granted	$ 37.81
Granted	$ 12.99
Granted	6 years 131 days
Forfeited	0 years
Forfeited (in Shares)
Forfeited
Forfeited
Exercised (in Shares)	(800,000)
Exercised	$ 18.60
Exercised	$ 6.86
Exercised	0 years

[1] As of September 30, 2012, 1.2 million of SARs outstanding were unvested. The Company expects that substantially all of these unvested awards will vest in future periods.

[2] As of September 30, 2012, total SARs outstanding had an intrinsic value of $45.4 million. SARs vested and exercisable had an intrinsic value of $25.5 million.