Securities Available-for-Sale - Additional Information (Detail) (USD $)	9 Months Ended
Sep. 30, 2014 security	Dec. 31, 2013 security
Investments, Debt and Equity Securities [Abstract]
Number of debt securities on which unrealized losses were primarily attributable to changes in interest	35	43
Unrealized losses reclassified out of accumulated other comprehensive income into earnings	$ 0
Carrying values of securities	$ 314,800,000	$ 243,200,000

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for FHLB debt obligations, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)(1)(i)

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

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