Additional Detail of Impaired Loans Broken Out According to Class (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Impaired loans with no a valuation allowance, recorded investment	$ 6,322	$ 4,702
Impaired loans with no related allowance, unpaid balance	6,361	4,702
Impaired loans with no related allowance	0	0
Impaired loans with no related allowance, average recorded investment YTD	5,138	2,894
Impaired loans with no related allowance, interest income recognized YTD	43	142
Impaired loans with a related allowance, recorded investment	4,510	4,858
Impaired loans with a related allowance, unpaid balance	4,510	4,858
Impaired loans with a related allowance	1,028	968
Impaired loans with a related allowance, average recored investment YTD	4,396	4,183
Impaired loans with a related allowance, interest income recognized YTD	123	114
Recorded Investment	10,832	9,560
Unpaid Balance	10,871	9,560
Related Allowance	1,028	968
Average Recorded Investment YTD	9,534	7,077
Interest Income Recognized YTD	166	256
Commercial installment
Financing Receivable, Impaired [Line Items]
Impaired loans with no a valuation allowance, recorded investment	0	0
Impaired loans with no related allowance, unpaid balance	0	0
Impaired loans with no related allowance	0	0
Impaired loans with no related allowance, average recorded investment YTD	3	50
Impaired loans with no related allowance, interest income recognized YTD	0	0
Impaired loans with a related allowance, recorded investment	268	240
Impaired loans with a related allowance, unpaid balance	268	240
Impaired loans with a related allowance	22	18
Impaired loans with a related allowance, average recored investment YTD	254	189
Impaired loans with a related allowance, interest income recognized YTD	10	20
Recorded Investment	268	240
Unpaid Balance	268	240
Related Allowance	22	18
Average Recorded Investment YTD	257	239
Interest Income Recognized YTD	10	20
Commercial real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with no a valuation allowance, recorded investment	6,077	4,665
Impaired loans with no related allowance, unpaid balance	6,116	4,665
Impaired loans with no related allowance	0	0
Impaired loans with no related allowance, average recorded investment YTD	4,927	2,654
Impaired loans with no related allowance, interest income recognized YTD	43	142
Impaired loans with a related allowance, recorded investment	3,232	2,558
Impaired loans with a related allowance, unpaid balance	3,232	2,558
Impaired loans with a related allowance	479	315
Impaired loans with a related allowance, average recored investment YTD	2,882	2,415
Impaired loans with a related allowance, interest income recognized YTD	102	59
Recorded Investment	9,309	7,223
Unpaid Balance	9,348	7,223
Related Allowance	479	315
Average Recorded Investment YTD	7,809	5,069
Interest Income Recognized YTD	145	201
Consumer real estate
Financing Receivable, Impaired [Line Items]
Impaired loans with no a valuation allowance, recorded investment	238	27
Impaired loans with no related allowance, unpaid balance	238	27
Impaired loans with no related allowance	0	0
Impaired loans with no related allowance, average recorded investment YTD	200	179
Impaired loans with no related allowance, interest income recognized YTD	0	0
Impaired loans with a related allowance, recorded investment	975	2,032
Impaired loans with a related allowance, unpaid balance	975	2,032
Impaired loans with a related allowance	501	607
Impaired loans with a related allowance, average recored investment YTD	1,230	1,546
Impaired loans with a related allowance, interest income recognized YTD	11	33
Recorded Investment	1,213	2,059
Unpaid Balance	1,213	2,059
Related Allowance	501	607
Average Recorded Investment YTD	1,430	1,725
Interest Income Recognized YTD	11	33
Consumer installment
Financing Receivable, Impaired [Line Items]
Impaired loans with no a valuation allowance, recorded investment	7	10
Impaired loans with no related allowance, unpaid balance	7	10
Impaired loans with no related allowance	0	0
Impaired loans with no related allowance, average recorded investment YTD	8	11
Impaired loans with no related allowance, interest income recognized YTD	0	0
Impaired loans with a related allowance, recorded investment	35	28
Impaired loans with a related allowance, unpaid balance	35	28
Impaired loans with a related allowance	26	28
Impaired loans with a related allowance, average recored investment YTD	30	33
Impaired loans with a related allowance, interest income recognized YTD	0	2
Recorded Investment	42	38
Unpaid Balance	42	38
Related Allowance	26	28
Average Recorded Investment YTD	38	44
Interest Income Recognized YTD	$ 0	$ 2

Amount of allowance for credit losses related to recorded investment.

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