Impaired Loans by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 2,063		$ 3,490
Unpaid Principal Balance	2,448		4,243
Average Recorded Investment	2,778	2,853
Interest Income Recognized	3	2
Interest Recognized-Cash Method	1	1
Recorded Investment	3,757		4,093
Unpaid Principal Balance	4,084		4,396
Related Allowance	1,497		1,652
Average Recorded Investment	3,926	4,517
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	1
Recorded Investment	5,820		7,583
Unpaid Principal Balance	6,532		8,639
Related Allowance	1,497		1,652
Average Recorded Investment	6,704	7,370
Interest Income Recognized	3	2
Interest Recognized-Cash Method	1	2
Residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	1,365		1,427
Unpaid Principal Balance	1,732		1,760
Average Recorded Investment	1,396	1,254
Interest Income Recognized	2	1
Interest Recognized-Cash Method	1	1
Recorded Investment	609		943
Unpaid Principal Balance	684		1,020
Related Allowance	143		213
Average Recorded Investment	776	921
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	1,974		2,370
Unpaid Principal Balance	2,416		2,780
Related Allowance	143		213
Average Recorded Investment	2,172	2,175
Interest Income Recognized	2	1
Interest Recognized-Cash Method	1	1
Land
Financing Receivable, Impaired [Line Items]
Recorded Investment	124		125
Unpaid Principal Balance	129		126
Average Recorded Investment	125	23
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	6		0
Unpaid Principal Balance	6		0
Related Allowance	6		0
Average Recorded Investment	3	0
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	130		125
Unpaid Principal Balance	135		126
Related Allowance	6		0
Average Recorded Investment	128	23
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment	260		403
Unpaid Principal Balance	272		413
Average Recorded Investment	332	257
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	260		403
Unpaid Principal Balance	272		413
Related Allowance	0		0
Average Recorded Investment	332	257
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Recorded Investment	72		1,535
Unpaid Principal Balance	73		1,944
Average Recorded Investment	804	1,233
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	1,334		1,301
Unpaid Principal Balance	1,453		1,394
Related Allowance	258		275
Average Recorded Investment	1,318	1,574
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	1,406		2,836
Unpaid Principal Balance	1,526		3,338
Related Allowance	258		275
Average Recorded Investment	2,122	2,807
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Commercial Business
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	1,776		1,776
Unpaid Principal Balance	1,909		1,909
Related Allowance	1,065		1,098
Average Recorded Investment	1,776	1,928
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	1,776		1,776
Unpaid Principal Balance	1,909		1,909
Related Allowance	1,065		1,098
Average Recorded Investment	1,776	1,928
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Home Equity and Second Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Investment	242		0
Unpaid Principal Balance	242		0
Average Recorded Investment	121	86
Interest Income Recognized	1	1
Interest Recognized-Cash Method	0	0
Recorded Investment	32		73
Unpaid Principal Balance	32		73
Related Allowance	25		66
Average Recorded Investment	53	94
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	1
Recorded Investment	274		73
Unpaid Principal Balance	274		73
Related Allowance	25		66
Average Recorded Investment	174	180
Interest Income Recognized	1	1
Interest Recognized-Cash Method	0	1
Other Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Interest Recognized-Cash Method	0	0
Recorded Investment	0		0
Unpaid Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Interest Recognized-Cash Method	$ 0	$ 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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+ 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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