Loans - Allowance for Loan Losses by Portfolio Segment and Related Recorded Investment in Loans (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in indemnification asset	$ 38,200	$ 49,400	$ 638
Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in allowance for losses related to impairment loans	$ 41,000	$ 52,400	$ 672

Change in carrying amount of the indemnification asset relating to loss sharing agreements with the Federal Deposit Insurance Corporation (FDIC). The change includes for example, but is not limited to, acquisitions, additional estimated losses, disposals, cash payments, accretion of discount and write-offs, net of recoveries.

No definition available.

Name:	us-gaap_FDICIndemnificationAssetPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration