Activity in Allowance for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses, beginning of period	$ 16,038	$ 16,815	$ 16,815
Provision charged to expense	950	1,350	6,025
Losses charged off	(1,100)	(1,867)	(8,002)
Recoveries	103	336	1,200
Allowance for loan losses, end of period	15,991	16,634	16,038
Allowance for loan losses, individually evaluated for impairment, ending balance	1,696		1,373
Allowance for loan losses, collectively evaluated for impairment, ending balance	14,295		14,665
Total allowance for loan losses	15,991	16,634	16,038
Loans, individually evaluated for impairment, ending balance	16,876		19,121
Loans, collectively evaluated for impairment, ending balance	958,681		971,448
Total loans	975,557		990,569
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses, beginning of period	9,908	10,602	10,602
Provision charged to expense	200	390	3,213
Losses charged off	(237)	(901)	(4,493)
Recoveries	2	153	586
Allowance for loan losses, end of period	9,873	10,244	9,908
Allowance for loan losses, individually evaluated for impairment, ending balance	1,639		1,316
Allowance for loan losses, collectively evaluated for impairment, ending balance	8,234		8,592
Total allowance for loan losses	9,873	10,244	9,908
Loans, individually evaluated for impairment, ending balance	13,702		15,704
Loans, collectively evaluated for impairment, ending balance	273,681		273,144
Total loans	287,383		288,848
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses, beginning of period	3,394	3,444	3,444
Provision charged to expense	500	465	1,612
Losses charged off	(383)	(441)	(1,901)
Recoveries	23	3	239
Allowance for loan losses, end of period	3,534	3,471	3,394
Allowance for loan losses, individually evaluated for impairment, ending balance	57		57
Allowance for loan losses, collectively evaluated for impairment, ending balance	3,477		3,337
Total allowance for loan losses	3,534	3,471	3,394
Loans, individually evaluated for impairment, ending balance	3,174		3,417
Loans, collectively evaluated for impairment, ending balance	487,959		499,202
Total loans	491,133		502,619
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses, beginning of period	2,736	2,769	2,769
Provision charged to expense	250	495	1,200
Losses charged off	(480)	(525)	(1,608)
Recoveries	78	180	375
Allowance for loan losses, end of period	2,584	2,919	2,736
Allowance for loan losses, collectively evaluated for impairment, ending balance	2,584		2,736
Total allowance for loan losses	2,584	2,919	2,736
Loans, collectively evaluated for impairment, ending balance	197,041		199,102
Total loans	$ 197,041		$ 199,102

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Reflects the gross amount charged against earnings during the period as credit losses (bad debt expense) based on review of the loan and lease portfolio and application of the methodology for estimating credit losses.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 114

-Paragraph 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Subparagraph d

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Reflects the amount of loans and leases that have been removed, or charged off, from both loan receivables and the reserve for credit losses, typically because they are considered to be not salvageable or have been purchased by unconsolidated collection entities.

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 8, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Name Staff Accounting Bulletin (SAB)

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-Section L

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Total of recoveries of amounts due the Entity that had previously been written off as uncollectible using allowances (the valuation accounts that are netted against the cost of an asset to value it at its carrying value) and total of reestablishments of reserves (liabilities established to represent expected future costs) that had previously been utilized.

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

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