Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended				3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Oct. 08, 2009	Sep. 30, 2012 Litigation Related to 2009 Exchange Offer [Member]	Jun. 30, 2012 Litigation Related to 2009 Exchange Offer [Member]	Dec. 31, 2012 Litigation Related to 2009 Exchange Offer [Member]	Dec. 31, 2012 Litigation Related to 2009 Exchange Offer [Member] Fidelity Settlement [Member]	Dec. 31, 2012 Litigation Related to 2009 Exchange Offer [Member] Other Shareholder Settlement [Member]	Dec. 31, 2012 Litigation Related to 2009 Exchange Offer [Member] Settlement With Remaining Class [Member]
Loss Contingencies [Line Items]
Rental expense	$ 16.7	$ 17.7	$ 16.9
Preferred stock, shares issued				9,336,905
Percentage of outstanding common stock to be held by parent company after merger	100.00%
Purported class actions filed							4
Fidelity Controlled Shares								6,111,879
Number of Shares Exchanged in Exchange Offer								6,933,526	310,690
Remaining Shares Permit To Participate In Settlement								821,647
Final Settlement Amount								22.5	1.0	9.2
Additional payments for settlement							4.2	4.0
Additional charge to the estimated costs of resolving the pending litigations					2.2	6.7	8.9
Amount not covered by insurance							$ 5