Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 1,222		$ 1,222		$ 3,490
Unpaid Principal Balance	1,497		1,497		4,243
Average Recorded Investment	1,567	2,777	2,173	2,814
Interest Income Recognized	6	2	11	5
Interest Recognized-Cash Method	4	1	6	4
Recorded Investment	3,457		3,457		4,093
Unpaid Principal Balance	3,832		3,832		4,396
Related Allowance	1,562		1,562		1,652
Average Recorded Investment	3,464	4,966	3,695	4,741
Interest Income Recognized	0	0	6	0
Interest Recognized-Cash Method	0	1	3	1
Recorded Investment	4,679		4,679		7,583
Unpaid Principal Balance	5,329		5,329		8,639
Related Allowance	1,562		1,562		1,652
Average Recorded Investment	5,031	7,743	5,868	7,555
Interest Income Recognized	6	2	17	5
Interest Recognized-Cash Method	4	2	9	5
Residential
Financing Receivable, Impaired [Line Items]
Recorded Investment	901		901		1,427
Unpaid Principal Balance	1,160		1,160		1,760
Average Recorded Investment	1,041	1,152	1,219	1,203
Interest Income Recognized	4	1	8	2
Interest Recognized-Cash Method	2	1	3	2
Recorded Investment	479		479		943
Unpaid Principal Balance	589		589		1,020
Related Allowance	95		95		213
Average Recorded Investment	560	1,382	668	1,151
Interest Income Recognized	0	0	1	0
Interest Recognized-Cash Method	0	1	0	1
Recorded Investment	1,380		1,380		2,370
Unpaid Principal Balance	1,749		1,749		2,780
Related Allowance	95		95		213
Average Recorded Investment	1,601	2,534	1,887	2,354
Interest Income Recognized	4	1	9	2
Interest Recognized-Cash Method	2	2	3	3
Land
Financing Receivable, Impaired [Line Items]
Recorded Investment	123		123		125
Unpaid Principal Balance	132		132		126
Average Recorded Investment	125	23	125	23
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	1
Recorded Investment	0		0		0
Unpaid Principal Balance	0		0		0
Related Allowance	0		0		0
Average Recorded Investment	0	0	2	0
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	123		123		125
Unpaid Principal Balance	132		132		126
Related Allowance	0		0		0
Average Recorded Investment	125	23	127	23
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	1
Construction
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0		403
Unpaid Principal Balance	0		0		413
Average Recorded Investment	102	330	217	293
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	0		0		403
Unpaid Principal Balance	0		0		413
Related Allowance	0		0		0
Average Recorded Investment	102	330	217	293
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	136		136		1,535
Unpaid Principal Balance	140		140		1,944
Average Recorded Investment	138	1,229	471	1,231
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	966		966		1,301
Unpaid Principal Balance	1,055		1,055		1,394
Related Allowance	144		144		275
Average Recorded Investment	977	1,630	1,147	1,602
Interest Income Recognized	0	0	0	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	1,102		1,102		2,836
Unpaid Principal Balance	1,195		1,195		3,338
Related Allowance	144		144		275
Average Recorded Investment	1,115	2,859	1,618	2,833
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		0
Unpaid Principal Balance	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	1,968		1,968		1,776
Unpaid Principal Balance	2,136		2,136		1,909
Related Allowance	1,315		1,315		1,098
Average Recorded Investment	1,872	1,826	1,824	1,877
Interest Income Recognized	0	0	4	0
Interest Recognized-Cash Method	0	0	3	0
Recorded Investment	1,968		1,968		1,776
Unpaid Principal Balance	2,136		2,136		1,909
Related Allowance	1,315		1,315		1,098
Average Recorded Investment	1,872	1,826	1,824	1,877
Interest Income Recognized	0	0	4	0
Interest Recognized-Cash Method	0	0	3	0
Home Equity and Second Mortgage
Financing Receivable, Impaired [Line Items]
Recorded Investment	62		62		0
Unpaid Principal Balance	65		65		0
Average Recorded Investment	161	43	141	64
Interest Income Recognized	2	0	3	2
Interest Recognized-Cash Method	2	0	3	1
Recorded Investment	44		44		73
Unpaid Principal Balance	52		52		73
Related Allowance	8		8		66
Average Recorded Investment	55	128	54	111
Interest Income Recognized	0	0	1	0
Interest Recognized-Cash Method	0	0	0	0
Recorded Investment	106		106		73
Unpaid Principal Balance	117		117		73
Related Allowance	8		8		66
Average Recorded Investment	216	171	195	175
Interest Income Recognized	2	0	4	2
Interest Recognized-Cash Method	2	0	3	1
Other Consumer
Financing Receivable, Impaired [Line Items]
Recorded Investment	0		0		0
Unpaid Principal Balance	0		0		0
Average Recorded Investment	0	0	0	0
Interest Income Recognized	0	1	0	1
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	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	1	0	1
Interest Recognized-Cash Method	$ 0	$ 0	$ 0	$ 0

Name:	us-gaap_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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=28368275&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=28368275&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant