Summary of Changes in SARs Outstanding (Parenthetical) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value, SARs outstanding	36.8
Intrinsic value, SARs vested and exercisable	18.3
Stock Appreciation Rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested SARs	2,500,000	[1],[2]	2,500,000
Stock Appreciation Rights | Unvested
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested SARs	1,400,000

[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.