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Short-term Borrowings - Interest Expense on Short-Term Borrowings (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Interest On Short Term Borrowings [Line Items] |  |  |
Total interest on short-term borrowings | $ 2,449us-gaap_InterestExpenseShortTermBorrowings | $ 1,262us-gaap_InterestExpenseShortTermBorrowings | $ 1,070us-gaap_InterestExpenseShortTermBorrowings
Federal funds purchased [Member] |  |  |
Interest On Short Term Borrowings [Line Items] |  |  |
Total interest on short-term borrowings | 42us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_FederalFundsPurchasedMember | 43us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_FederalFundsPurchasedMember | 128us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_FederalFundsPurchasedMember
Borrowings from FHLB [Member] |  |  |
Interest On Short Term Borrowings [Line Items] |  |  |
Total interest on short-term borrowings | 2,019us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember | 893us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember | 545us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember
Securities sold under agreements to repurchase [Member] |  |  |
Interest On Short Term Borrowings [Line Items] |  |  |
Total interest on short-term borrowings | $ 388us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember | $ 326us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember | $ 397us-gaap_InterestExpenseShortTermBorrowings / us-gaap_ShortTermDebtTypeAxis = us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseMember

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- Definition The aggregate interest expense incurred on short-term borrowings including commercial paper and Federal funds purchased and securities sold under agreements to repurchase. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.7) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 7 -Article 9 + Details
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