Securities Sold under Agreements to Repurchase - Additional Information (Detail) (U.S. Government Sponsored Enterprises [Member], USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
U.S. Government Sponsored Enterprises [Member]
Assets Sold under Agreements to Repurchase [Line Items]
U.S. Government Sponsored Enterprise securities with a total amortized cost	$ 213,817,000	$ 216,747,000	$ 187,995,000
Fair value of the collateral repurchase agreement	$ 212,255,000	$ 213,350,000	$ 191,704,000

The carrying value as of the balance sheet date of securities received as collateral from a counterparty that were re-pledged, sold, delivered or otherwise reused by the entity.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=34720971&loc=SL6224234-111729

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