Impaired Loans by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 2,877		$ 2,877		$ 2,703
Unpaid Principal Balance	3,449		3,449		3,136
Average Recorded Investment	2,777	1,442	2,814	1,585
Interest Income Recognized	2	17	5	30
Interest Recognized-Cash Method	1	15	4	20
Recorded Investment	5,115		5,115		4,698
Unpaid Principal Balance	5,380		5,380		5,189
Related Allowance	1,651		1,651		1,658
Average Recorded Investment	4,966	5,731	4,741	5,852
Interest Income Recognized	0	5	0	0
Interest Recognized-Cash Method	1	0	1	36
Recorded Investment	7,992		7,992		7,401
Unpaid Principal Balance	8,829		8,829		8,325
Related Allowance	1,651		1,651		1,658
Average Recorded Investment	7,743	7,173	7,555	7,437
Interest Income Recognized	2	22	5	30
Interest Recognized-Cash Method	2	15	5	56
Residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,259		1,259
Unpaid Principal Balance	1,531		1,531
Average Recorded Investment	1,152	820	1,203	936
Interest Income Recognized	1	3	2	13
Interest Recognized-Cash Method	1	2	2	5
Recorded Investment	1,439		1,439
Unpaid Principal Balance	1,524		1,524
Related Allowance	267		267
Average Recorded Investment	1,382	2,481	1,151	2,260
Interest Income Recognized	0	5	0	0
Interest Recognized-Cash Method	1	0	1	36
Recorded Investment	2,698		2,698
Unpaid Principal Balance	3,055		3,055
Related Allowance	267		267
Average Recorded Investment	2,534	3,301	2,354	3,196
Interest Income Recognized	1	8	2	13
Interest Recognized-Cash Method	2	2	3	41
Land
Financing Receivable, Impaired [Line Items]
Recorded Investment	4		4		5
Unpaid Principal Balance	5		5		6
Average Recorded Investment	23	6	23	5
Interest Income Recognized	0	1	0	1
Interest Recognized-Cash Method	0	3	1	3
Recorded Investment	0		0		0
Unpaid Principal Balance	0		0		0
Related Allowance	0		0		0
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	4		4		5
Unpaid Principal Balance	5		5		6
Related Allowance	0		0		0
Average Recorded Investment	23	6	23	5
Interest Income Recognized	0	1	0	1
Interest Recognized-Cash Method	0	3	1	3
Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment	394		394
Unpaid Principal Balance	402		402
Average Recorded Investment	330	331	293	264
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	0	0	70
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	394		394
Unpaid Principal Balance	402		402
Related Allowance	0		0
Average Recorded Investment	330	331	293	334
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,220		1,220
Unpaid Principal Balance	1,511		1,511
Average Recorded Investment	1,229	241	1,231	339
Interest Income Recognized	0	9	0	9
Interest Recognized-Cash Method	0	9	0	9
Recorded Investment	1,766		1,766
Unpaid Principal Balance	1,845		1,845
Related Allowance	441		441
Average Recorded Investment	1,630	1,004	1,602	1,101
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	2,986		2,986
Unpaid Principal Balance	3,356		3,356
Related Allowance	441		441
Average Recorded Investment	2,859	1,245	2,833	1,440
Interest Income Recognized	0	9	0	9
Interest Recognized-Cash Method	0	9	0	9
Commercial Business
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	0	25	0	17
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	1,809		1,809
Unpaid Principal Balance	1,909		1,909
Related Allowance	914		914
Average Recorded Investment	1,826	1,981	1,877	2,063
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	1,809		1,809
Unpaid Principal Balance	1,909		1,909
Related Allowance	914		914
Average Recorded Investment	1,826	2,006	1,877	2,080
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Home Equity and Second Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	43	16	64	18
Interest Income Recognized	0	2	2	4
Interest Recognized-Cash Method	0	1	1	2
Recorded Investment	101		101
Unpaid Principal Balance	102		102
Related Allowance	29		29
Average Recorded Investment	128	265	111	352
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	101		101
Unpaid Principal Balance	102		102
Related Allowance	29		29
Average Recorded Investment	171	281	175	370
Interest Income Recognized	0	2	2	4
Interest Recognized-Cash Method	0	1	1	2
Other Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	0	3	0	6
Interest Income Recognized	1	2	1	3
Interest Recognized-Cash Method	0	0	0	1
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	0	0	6
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	3	0	12
Interest Income Recognized	1	2	1	3
Interest Recognized-Cash Method	0	0	0	1
Residential Real Estate
Financing Receivable, Impaired [Line Items]
Recorded Investment					1,149
Unpaid Principal Balance					1,507
Recorded Investment					1,132
Unpaid Principal Balance					1,233
Related Allowance					183
Recorded Investment					2,281
Unpaid Principal Balance					2,740
Related Allowance					183
Commercial Real Estate Construction Financing Receivable
Financing Receivable, Impaired [Line Items]
Recorded Investment					247
Unpaid Principal Balance					249
Recorded Investment					0
Unpaid Principal Balance					0
Related Allowance					0
Recorded Investment					247
Unpaid Principal Balance					249
Related Allowance					0
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Recorded Investment					1,215
Unpaid Principal Balance					1,280
Recorded Investment					1,638
Unpaid Principal Balance					1,933
Related Allowance					539
Recorded Investment					2,853
Unpaid Principal Balance					3,213
Related Allowance					539
Commercial Leases
Financing Receivable, Impaired [Line Items]
Recorded Investment					0
Unpaid Principal Balance					0
Recorded Investment					1,928
Unpaid Principal Balance					2,023
Related Allowance					936
Recorded Investment					1,928
Unpaid Principal Balance					2,023
Related Allowance					936
Home Equity Line of Credit
Financing Receivable, Impaired [Line Items]
Recorded Investment					87
Unpaid Principal Balance					94
Recorded Investment					0
Unpaid Principal Balance					0
Related Allowance					0
Recorded Investment					87
Unpaid Principal Balance					94
Related Allowance					0
Other Consumer Loans and Leases
Financing Receivable, Impaired [Line Items]
Recorded Investment					0
Unpaid Principal Balance					0
Recorded Investment					0
Unpaid Principal Balance					0
Related Allowance					0
Recorded Investment					0
Unpaid Principal Balance					0
Related Allowance					$ 0

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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

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-SubTopic 10

-Section 50

-Paragraph 17

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

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