Allowance for Loan Losses - Additional Information (Detail) (Non-Covered Loans, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Non-Covered Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Non-accrual loans	$ 246,568	$ 325,815

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5111-111524

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant