Financial Instruments - Notional and Fair Values of TBA's (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
FHA loan commitments balance	$ 297.5	$ 326.7
OMHHF had a loan receivable balance (included in other assets)	$ 56.3	$ 109.3

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount that a bank with insufficient reserves at a Federal Reserve Bank borrows, at the federal funds rate, from another bank to meet its reserve requirements for that day and the amount of securities that an institution sells and agrees to repurchase at a specified date for a specified price, net of any reductions or offsets.

No definition available.

Name:	us-gaap_FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant