Loans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding principal balance of acquired impaired loans	$ 198.34	$ 7.71
Commitments to extend credit including availability on lines of credit	215.77	194.27
Standby letters of credit and financial guarantees	6.81	2.90
Gross notional amounts of outstanding commitments	14.84	9.15
Loans to related parties	16.62	18.41
Loans to related parties, additions	2.58
Loans to related parties, repayments	1.58
Loan to related parties, decreases	2.79
Customer overdraft	$ 1.55	$ 1.48

Gross notional amounts of outstanding commitments.

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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

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This item represents a non-contingent liability for the fair value of an obligation to stand ready to perform over the term of a guaranty issued in the event that specified triggering events or conditions occur.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

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Reflects the amount of new advances made to related parties in the form of loan and lease receivables.

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Reflects the amount of collections received from related parties to reduce the carrying amounts of loans and leases receivable due from them.

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Reflects the sum for the period of the additions and reductions to related party loans, which when added to the opening balance of related party loan will agree to the ending balance of such loans. This subtotal typically is not reflected.

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