Summary of Changes in SARs Outstanding (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Year
Weighted Average Remaining Contractual Term
Granted	1.0
Stock Appreciation Rights
SARs
Beginning Balance	2,500,000
Granted	400,000
Forfeited
Exercised	(400,000)
Ending Balance	2,500,000	[1],[2]
Vested and exercisable at December 31, 2011	1,100,000	[2]
Per Share Weighted Average Exercise Price
Beginning Balance	17.22
Granted	38.05
Forfeited
Exercised	38.26
Ending Balance	20.39	[1],[2]
Vested and exercisable at December 31, 2011	18.07	[2]
Per Share Weighted Average Grant Date Fair Value
Beginning Balance	6.62
Granted	13.58
Forfeited
Exercised	6.38
Ending Balance	7.66	[1],[2]
Vested and exercisable at December 31, 2011	6.77	[2]
Weighted Average Remaining Contractual Term
Beginning Balance	4.55
Granted	6.15
Forfeited
Exercised
Ending Balance	4.00	[1],[2]
Vested and exercisable at December 31, 2011	2.96	[2]

[1] At December 31, 2011, 1.4 million of the SARs were unvested. The Company expects that substantially all of these unvested awards will vest in future periods.

[2] At December 31, 2011, SARs outstanding had an intrinsic value of $36.8 million. SARs vested and exercisable had an intrinsic value of $18.3 million.