Summary of Impaired Loan Balances and Associated Allowance by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 4,732	$ 4,732	$ 5,532
Recorded Investment	22,753	22,753	21,854
Unpaid Principal Balance	7,261	7,261	7,655
Unpaid Principal Balance	22,753	22,753	22,424
Related Allowance
Average Recorded Investment	4,767	4,142	4,758
Interest Income Recognized	6	13	21
Recorded Investment	27,485	27,485	27,386
Unpaid Principal Balance	30,014	30,014	30,079
Related Allowance	3,785	3,785	3,671
Average Recorded Investment	27,686	27,950	28,821
Average Recorded Investment	22,919	23,808	24,063
Interest Income Recognized	31	70	141
Interest Income Recognized	25	57	120
Residential real estate loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	2,087	2,087	1,998
Recorded Investment	11,371	11,371	10,717
Unpaid Principal Balance	2,536	2,536	1,810
Unpaid Principal Balance	11,371	11,371	11,287
Related Allowance
Average Recorded Investment	2,024	2,081	1,847
Interest Income Recognized	6	13	21
Related Allowance	1,903	1,903	1,364
Average Recorded Investment	11,151	11,360	11,280
Interest Income Recognized	25	57	109
Commercial real estate loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,769	1,769	2,353
Recorded Investment	5,593	5,593	5,477
Unpaid Principal Balance	2,571	2,571	3,815
Unpaid Principal Balance	5,593	5,593	5,478
Related Allowance
Average Recorded Investment	1,654	1,009	2,078
Related Allowance	707	707	961
Average Recorded Investment	5,919	6,433	7,257
Interest Income Recognized			3
Commercial loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	279	279	383
Recorded Investment	4,472	4,472	3,636
Unpaid Principal Balance	526	526	665
Unpaid Principal Balance	4,472	4,472	3,636
Related Allowance
Average Recorded Investment	289	260	393
Related Allowance	933	933	815
Average Recorded Investment	4,162	4,590	3,963
Interest Income Recognized			7
Home equity loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	591	591	782
Recorded Investment	1,060	1,060	1,888
Unpaid Principal Balance	1,462	1,462	1,189
Unpaid Principal Balance	1,060	1,060	1,887
Related Allowance
Average Recorded Investment	793	787	422
Related Allowance	203	203	440
Average Recorded Investment	1,465	1,165	1,457
Interest Income Recognized			1
Consumer loans
Financing Receivable, Impaired [Line Items]
Recorded Investment	6	6	16
Recorded Investment	257	257	136
Unpaid Principal Balance	166	166	176
Unpaid Principal Balance	257	257	136
Related Allowance
Average Recorded Investment	7	5	18
Related Allowance	39	39	91
Average Recorded Investment	$ 222	$ 260	$ 106

Impaired Financing Receivable, With No Related Allowance, Related Allowance

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5258-111524

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+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953550-111524

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