Impaired Loans by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 2,673		$ 2,673		$ 2,703
Unpaid Principal Balance	3,248		3,248		3,136
Average Recorded Investment	2,838	1,849	2,792	1,731
Interest Income Recognized	1	9	3	13
Interest Recognized-Cash Method	1	3	2	5
Recorded Investment	4,815		4,815		4,698
Unpaid Principal Balance	5,068		5,068		5,189
Related Allowance	1,622		1,622		1,658
Average Recorded Investment	4,575	5,734	4,615	5,966
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	1	34	1	34
Recorded Investment	7,488		7,488		7,401
Unpaid Principal Balance	8,316		8,316		8,325
Related Allowance	1,622		1,622		1,658
Average Recorded Investment	7,413	7,583	7,407	7,697
Interest Income Recognized	1	9	3	13
Interest Recognized-Cash Method	2	37	3	39
Residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,045		1,045
Unpaid Principal Balance	1,314		1,314
Average Recorded Investment	1,202	947	1,184	977
Interest Income Recognized	0	6	1	10
Interest Recognized-Cash Method	1	2	1	4
Recorded Investment	1,325		1,325
Unpaid Principal Balance	1,410		1,410
Related Allowance	231		231
Average Recorded Investment	1,017	2,156	1,055	2,187
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	34	0	34
Recorded Investment	2,370		2,370
Unpaid Principal Balance	2,724		2,724
Related Allowance	231		231
Average Recorded Investment	2,219	3,103	2,239	3,164
Interest Income Recognized	0	6	1	10
Interest Recognized-Cash Method	1	36	1	38
Land
Financing Receivable, Impaired [Line Items]
Recorded Investment	41		41		5
Unpaid Principal Balance	42		42		6
Average Recorded Investment	41	6	29	4
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
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	41		41		5
Unpaid Principal Balance	42		42		6
Related Allowance	0		0		0
Average Recorded Investment	41	6	29	4
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment	265		265
Unpaid Principal Balance	270		270
Average Recorded Investment	266	441	259	294
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	93
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	265		265
Unpaid Principal Balance	270		270
Related Allowance	0		0
Average Recorded Investment	266	441	259	387
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	1,237		1,237
Unpaid Principal Balance	1,530		1,530
Average Recorded Investment	1,244	438	1,234	424
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	1,493		1,493
Unpaid Principal Balance	1,593		1,593
Related Allowance	348		348
Average Recorded Investment	1,502	1,011	1,547	1,134
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	2,730		2,730
Unpaid Principal Balance	3,123		3,123
Related Allowance	348		348
Average Recorded Investment	2,746	1,449	2,781	1,558
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Commercial Business
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	0	0	0	7
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	1,843		1,843
Unpaid Principal Balance	1,909		1,909
Related Allowance	914		914
Average Recorded Investment	1,885	2,071	1,899	2,097
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	1,843		1,843
Unpaid Principal Balance	1,909		1,909
Related Allowance	914		914
Average Recorded Investment	1,885	2,071	1,899	2,104
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	85		85
Unpaid Principal Balance	92		92
Average Recorded Investment	85	17	86	19
Interest Income Recognized	1	2	2	2
Interest Recognized-Cash Method	0	0	1	0
Recorded Investment	154		154
Unpaid Principal Balance	156		156
Related Allowance	129		129
Average Recorded Investment	171	484	114	447
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	1	0	1	0
Recorded Investment	239		239
Unpaid Principal Balance	248		248
Related Allowance	129		129
Average Recorded Investment	256	501	200	466
Interest Income Recognized	1	2	2	2
Interest Recognized-Cash Method	1	0	2	0
Other Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	0	0	0	6
Interest Income Recognized	0	1	0	1
Interest Recognized-Cash Method	0	1	0	1
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	12	0	8
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	12	0	14
Interest Income Recognized	0	1	0	1
Interest Recognized-Cash Method	0	1	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

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

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

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