Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012
Fair Value Disclosures [Abstract]
Impaired loans recognized	$ (14,000)	$ (212,000)
Transfers between level 1 and 2	0	0
Liabilities measured at fair value on a recurring or nonrecurring basis	0	0
Amortized cost of Level 3 securities	41,204,000	41,204,000	65,020,000
Unrealized loss	$ 725,000	$ 725,000	$ 960,000

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

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=25499696&loc=d3e19207-110258

Name:	us-gaap_FairValueAssetsLevel1ToLevel2TransfersAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant