Summary Of Changes In SARs Outstanding (Parenthetical) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value, SARs outstanding	48.9
Intrinsic value, SARs vested and exercisable	32.9
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	1,200,000

[1] Total SARs outstanding had an intrinsic value of $48.9 million. SARs vested and exercisable had an intrinsic value of $32.9 million.

[2] As of March 31, 2012, 1.2 million of the SARs outstanding were unvested. The Company expects that substantially all of these unvested awards will vest in future periods.