Fair Value - Additional Information (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Fair Value of Financial Instruments [Line Items]
Impaired loans	$ 40,702,000	$ 48,773,000
Impaired Loans Fair Value	36,700,000	43,600,000
Specific loan loss Reserves	$ 4,000,000	$ 5,200,000

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953550-111524

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