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, 2012	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	$ 1,302	$ 1,302	$ 2,791
Impaired loans with no related allowance, unpaid balance	1,302	1,302	2,791
Impaired loans with no related allowance:	1,302	1,302	2,791
Impaired loans with no related allowance, average recorded investment YTD		1,266	1,825
Impaired loans with no related allowance, interest income recognized YTD		13	93
Impaired loans with a related allowance , recorded investment	1,833	1,833	2,334
Impaired loans with a related allowance , unpaid balance	1,833	1,833	2,334
Impaired loans with a related allowance:	771	771	738
Impaired loans with a related allowance , average recored investment YTD		1,453	2,360
Impaired loans with a related allowance , interest income recognized YTD		26	41
Recorded Investment	3,135	3,135	5,125
Unpaid Balance	3,135	3,135	5,125
Related Allowance	771	771	738
Average Recorded Investment YTD	2,719	2,690	4,185
Interest Income Recognized YTD	7	39	134
Commercial installment
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	76	76	121
Impaired loans with no related allowance, unpaid balance	76	76	121
Impaired loans with no related allowance:	76	76	121
Impaired loans with no related allowance, average recorded investment YTD		76	69
Impaired loans with no related allowance, interest income recognized YTD		0	5
Impaired loans with a related allowance , recorded investment	145	145	125
Impaired loans with a related allowance , unpaid balance	145	145	125
Impaired loans with a related allowance:	55	55	63
Impaired loans with a related allowance , average recored investment YTD		164	128
Impaired loans with a related allowance , interest income recognized YTD		5
Recorded Investment	221	221	246
Unpaid Balance	221	221	246
Related Allowance	55	55	63
Average Recorded Investment YTD		240	197
Interest Income Recognized YTD		5	5
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	993	993	2,420
Impaired loans with no related allowance, unpaid balance	993	993	2,420
Impaired loans with no related allowance:	993	993	2,420
Impaired loans with no related allowance, average recorded investment YTD		957	1,457
Impaired loans with no related allowance, interest income recognized YTD		3	85
Impaired loans with a related allowance , recorded investment	1,544	1,544	1,533
Impaired loans with a related allowance , unpaid balance	1,544	1,544	1,533
Impaired loans with a related allowance:	637	637	571
Impaired loans with a related allowance , average recored investment YTD		1,079	1,463
Impaired loans with a related allowance , interest income recognized YTD		18	23
Recorded Investment	2,537	2,537	3,953
Unpaid Balance	2,537	2,537	3,953
Related Allowance	637	637	571
Average Recorded Investment YTD		2,036	2,920
Interest Income Recognized YTD	7	21	108
Consumer real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	231	231	241
Impaired loans with no related allowance, unpaid balance	231	231	241
Impaired loans with no related allowance:	231	231	241
Impaired loans with no related allowance, average recorded investment YTD		231	288
Impaired loans with no related allowance, interest income recognized YTD		10	3
Impaired loans with a related allowance , recorded investment	99	99	647
Impaired loans with a related allowance , unpaid balance	99	99	647
Impaired loans with a related allowance:	35	35	91
Impaired loans with a related allowance , average recored investment YTD		175	740
Impaired loans with a related allowance , interest income recognized YTD		2	12
Recorded Investment	330	330	888
Unpaid Balance	330	330	888
Related Allowance	35	35	91
Average Recorded Investment YTD		406	1,028
Interest Income Recognized YTD		12	15
Consumer installment
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, recorded investment	2	2	9
Impaired loans with no related allowance, unpaid balance	2	2	9
Impaired loans with no related allowance:	2	2	9
Impaired loans with no related allowance, average recorded investment YTD		2	11
Impaired loans with no related allowance, interest income recognized YTD		0
Impaired loans with a related allowance , recorded investment	45	45	29
Impaired loans with a related allowance , unpaid balance	45	45	29
Impaired loans with a related allowance:	44	44	13
Impaired loans with a related allowance , average recored investment YTD		35	29
Impaired loans with a related allowance , interest income recognized YTD		1	6
Recorded Investment	47	47	38
Unpaid Balance	47	47	38
Related Allowance	44	44	13
Average Recorded Investment YTD		37	40
Interest Income Recognized YTD		$ 1	$ 6

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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

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-SubTopic 10

-Section 50

-Paragraph 15

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