Financial Instruments - Effects of Derivative Financial Instruments on Consolidated Statements of Income and Comprehensive Income (Detail) (Interest Rate Swap [Member], Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Other Comprehensive Income (OCI) (Effective Portion)		[1]		[1]		[1]
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified from OCI to Income (Effective Portion)		[1]		[1]	$ (0.9)	[1]

[1] Effective March 11, 2010 (the closing date of the 2010 refinancing of the 2006 bank term loan facility), the 2008 Interest Rate Swap, which expired in April 2010, was no longer designated as a cash flow hedge. (See "Interest Rate Swap" in this Note 12).