Debt (Detail) - Borrowings (Parentheticals) (USD $) In Millions, unless otherwise specified				9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012 Bank Term Loan [Member]
Eurodollar base rate				0.36%
Margin				1.50%
Notional fixed-for-floating interest rate swap contract (in Dollars)	$ 200.0
Debt, effective annual interest rate	3.76%	3.76%
Revolver, additional borrowing capacity (in Dollars)	$ 354.2		$ 150.0