Fair Value Measurements - Additional Information (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Fair Value Disclosures [Abstract]
Fair value Level 2 to Level 1 transfers amount	$ 35,008,000
Impaired non-covered loans with an outstanding balance	6,624,000	7,269,000
Reserve in allowance for credit losses	$ 329,000	$ 880,000

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bb)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Name:	us-gaap_FairValueAssetsLevel2ToLevel1TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant