Summary Of Changes In SARs Outstanding (Parenthetical) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value, SARs outstanding	47.5
Intrinsic value, SARs vested and exercisable	31.1
Stock Appreciation Rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested SARs	2,400,000	[1],[2]	2,500,000
Unvested | Stock Appreciation Rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested SARs	1,100,000

[1] As of June 30, 2012, 1.1 million of the SARs outstanding were unvested. The Company expects that substantially all of these unvested awards will vest in future periods.

[2] As of June 30, 2012, total SARs outstanding had an intrinsic value of $47.5 million. SARs vested and exercisable had an intrinsic value of $31.1 million.