Long Term Debt (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		12 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2012 Series A Notes	Dec. 31, 2011 Series A Notes	Dec. 31, 2012 Series B Notes	Dec. 31, 2011 Series B Notes	Dec. 31, 2012 Series C Notes	Oct. 31, 2012 Term Loan	Dec. 31, 2012 Term Loan	Dec. 31, 2012 Term A Loan
Debt Instrument [Line Items]
Principal amount	$ 35.0	$ 35.0	$ 30.0	$ 30.0	$ 35.0		$ 150.0	$ 60.0
Term Loan principal payments plus accrued interest payable, quarterly							$ 7.5	$ 3.0
Senior long-term notes, interest rate	6.07%	6.07%	6.28%		6.49%
Eurodollar Rate plus the applicable percentage								2.72%
Maturity date	Mar. 25, 2013		Mar. 25, 2014		Mar. 25, 2015	Oct. 26, 2017	Mar. 26, 2013	Oct. 26, 2017