Additional Detail of Impaired Loans Broken Out According to Class (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Impaired loans without a valuation allowance, recorded investment	$ 1,850	$ 1,850	$ 1,445
Impaired loans with no related allowance, unpaid balance	1,908	1,908	2,824
Impaired loans with no related allowance, average recorded investment YTD		1,329	1,374
Impaired loans with no related allowance, interest income recognized YTD		58	48
Impaired loans with a related allowance, recorded investment	2,501	2,501	2,144
Impaired loans with a related allowance, unpaid balance	2,571	2,571	2,144
Impaired loans with a related allowance:	748	748	936
Impaired loans with a related allowance, average recored investment YTD		2,225	1,988
Impaired loans with a related allowance, interest income recognized YTD		52	52
Recorded Investment	4,351	4,351	3,589
Unpaid Balance	4,479	4,479	4,968
Related Allowance	748	748	936
Average Recorded Investment YTD	3,554	3,554	2,979
Interest Income Recognized YTD	24	42	100
Commercial installment
Financing Receivable, Impaired [Line Items]
Impaired loans without a valuation allowance, recorded investment	4	4	15
Impaired loans with no related allowance, unpaid balance	4	4	15
Impaired loans with no related allowance, average recorded investment YTD		50	46
Impaired loans with no related allowance, interest income recognized YTD		0	0
Impaired loans with a related allowance, recorded investment	87	87	203
Impaired loans with a related allowance, unpaid balance	87	87	203
Impaired loans with a related allowance:	32	32	73
Impaired loans with a related allowance, average recored investment YTD		60	173
Impaired loans with a related allowance, interest income recognized YTD		5	8
Recorded Investment	91	91	218
Unpaid Balance	91	91	218
Related Allowance	32	32	73
Average Recorded Investment YTD		110	219
Interest Income Recognized YTD		5	8
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Impaired loans without a valuation allowance, recorded investment	1,715	1,715	1,013
Impaired loans with no related allowance, unpaid balance	1,773	1,773	1,529
Impaired loans with no related allowance, average recorded investment YTD		1,129	1,004
Impaired loans with no related allowance, interest income recognized YTD		56	39
Impaired loans with a related allowance, recorded investment	1,610	1,610	1,549
Impaired loans with a related allowance, unpaid balance	1,680	1,680	1,549
Impaired loans with a related allowance:	391	391	747
Impaired loans with a related allowance, average recored investment YTD		1,308	1,546
Impaired loans with a related allowance, interest income recognized YTD		33	38
Recorded Investment	3,325	3,325	2,562
Unpaid Balance	3,453	3,453	3,078
Related Allowance	391	391	747
Average Recorded Investment YTD		2,437	2,550
Interest Income Recognized YTD	24	41	77
Consumer real estate
Financing Receivable, Impaired [Line Items]
Impaired loans without a valuation allowance, recorded investment	126	126	106
Impaired loans with no related allowance, unpaid balance	126	126	969
Impaired loans with no related allowance, average recorded investment YTD		145	168
Impaired loans with no related allowance, interest income recognized YTD		2	8
Impaired loans with a related allowance, recorded investment	768	768	44
Impaired loans with a related allowance, unpaid balance	768	768	44
Impaired loans with a related allowance:	289	289	44
Impaired loans with a related allowance, average recored investment YTD		820	72
Impaired loans with a related allowance, interest income recognized YTD		12	4
Recorded Investment	894	894	150
Unpaid Balance	894	894	1,013
Related Allowance	289	289	44
Average Recorded Investment YTD		965	240
Interest Income Recognized YTD	0	1	12
Consumer installment
Financing Receivable, Impaired [Line Items]
Impaired loans without a valuation allowance, recorded investment	5	5	311
Impaired loans with no related allowance, unpaid balance	5	5	311
Impaired loans with no related allowance, average recorded investment YTD		5	156
Impaired loans with no related allowance, interest income recognized YTD		0	1
Impaired loans with a related allowance, recorded investment	36	36	348
Impaired loans with a related allowance, unpaid balance	36	36	348
Impaired loans with a related allowance:	36	36	72
Impaired loans with a related allowance, average recored investment YTD		37	197
Impaired loans with a related allowance, interest income recognized YTD		2	2
Recorded Investment	41	41	659
Unpaid Balance	41	41	659
Related Allowance	36	36	72
Average Recorded Investment YTD		42	353
Interest Income Recognized YTD		$ 2	$ 3

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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=28368275&loc=d3e5212-111524

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

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