Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Commercial
Financing Receivable, Impaired [Line Items]
Recorded Balance	$ 96		$ 96		$ 112
Unpaid Principal Balance	96		96		112
Specific Allowance	84		84		92
Average Investment in Impaired Loans	98	$ 416	101	$ 429
Interest Income Recognized	1	19	5	24
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	1,496		1,496		1,756
Unpaid Principal Balance	1,496		1,496		2,106
Specific Allowance	331		331		622
Average Investment in Impaired Loans	1,972	5,537	2,240	5,632
Interest Income Recognized	14	135	58	270
Residential
Financing Receivable, Impaired [Line Items]
Recorded Balance	0		0		0
Unpaid Principal Balance	0		0		0
Specific Allowance	0		0		0
Average Investment in Impaired Loans	0	0	0	0
Interest Income Recognized	0	0	0	0
Installment
Financing Receivable, Impaired [Line Items]
Recorded Balance	224		224		0
Unpaid Principal Balance	224		224		0
Specific Allowance	129		129		0
Average Investment in Impaired Loans	235	0	237	0
Interest Income Recognized	10	0	14	0
Loans without a specific valuation allowance
Financing Receivable, Impaired [Line Items]
Recorded Balance	507		507		801
Unpaid Principal Balance	507		507		1,151
Specific Allowance	0		0		0
Average Investment in Impaired Loans	895	1,795	1,162	1,821
Interest Income Recognized	5	59	31	74
Loans without a specific valuation allowance | Commercial
Financing Receivable, Impaired [Line Items]
Recorded Balance	0		0		7
Unpaid Principal Balance	0		0		7
Specific Allowance	0		0		0
Average Investment in Impaired Loans	0	9	0	12
Interest Income Recognized	0	0	0	1
Loans without a specific valuation allowance | Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	507		507		794
Unpaid Principal Balance	507		507		1,144
Specific Allowance	0		0		0
Average Investment in Impaired Loans	895	1,786	1,162	1,809
Interest Income Recognized	5	59	31	73
Loans without a specific valuation allowance | Residential
Financing Receivable, Impaired [Line Items]
Recorded Balance	0		0		0
Unpaid Principal Balance	0		0		0
Specific Allowance	0		0		0
Average Investment in Impaired Loans	0	0	0	0
Interest Income Recognized	0	0	0	0
Loans without a specific valuation allowance | Installment
Financing Receivable, Impaired [Line Items]
Recorded Balance	0		0		0
Unpaid Principal Balance	0		0		0
Specific Allowance	0		0		0
Average Investment in Impaired Loans	0	0	0	0
Interest Income Recognized	0	0	0	0
Loans with a specific valuation allowance
Financing Receivable, Impaired [Line Items]
Recorded Balance	1,309		1,309		1,067
Unpaid Principal Balance	1,309		1,309		1,067
Specific Allowance	544		544		714
Average Investment in Impaired Loans	1,410	4,158	1,416	4,240
Interest Income Recognized	20	95	46	220
Loans with a specific valuation allowance | Commercial
Financing Receivable, Impaired [Line Items]
Recorded Balance	96		96		105
Unpaid Principal Balance	96		96		105
Specific Allowance	84		84		92
Average Investment in Impaired Loans	98	407	101	417
Interest Income Recognized	1	19	5	23
Loans with a specific valuation allowance | Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	989		989		962
Unpaid Principal Balance	989		989		962
Specific Allowance	331		331		622
Average Investment in Impaired Loans	1,077	3,751	1,078	3,823
Interest Income Recognized	9	76	27	197
Loans with a specific valuation allowance | Residential
Financing Receivable, Impaired [Line Items]
Recorded Balance	0		0		0
Unpaid Principal Balance	0		0		0
Specific Allowance	0		0		0
Average Investment in Impaired Loans	0	0	0	0
Interest Income Recognized	0	0	0	0
Loans with a specific valuation allowance | Installment
Financing Receivable, Impaired [Line Items]
Recorded Balance	224		224		0
Unpaid Principal Balance	224		224		0
Specific Allowance	129		129		$ 0
Average Investment in Impaired Loans	235	0	237	0
Interest Income Recognized	$ 10	$ 0	$ 14	$ 0