Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Commercial
Financing Receivable, Impaired [Line Items]
Recorded Balance	$ 98		$ 98		$ 112
Unpaid Principal Balance	98		98		112
Specific Allowance	86		86		92
Average Investment in Impaired Loans	100	$ 518	102	$ 536
Interest Income Recognized	2	3	4	5
Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	1,947		1,947		1,756
Unpaid Principal Balance	1,947		1,947		2,106
Specific Allowance	377		377		622
Average Investment in Impaired Loans	2,421	6,231	2,445	5,397
Interest Income Recognized	20	84	44	135
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	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
Financing Receivable, Impaired [Line Items]
Recorded Balance	1,064		1,064		801
Unpaid Principal Balance	1,064		1,064		1,151
Specific Allowance	0		0		0
Average Investment in Impaired Loans	1,493	780	1,500	788
Interest Income Recognized	17	7	26	15
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	96	0	97
Interest Income Recognized	0	1	0	1
Loans without a specific valuation allowance | Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	1,064		1,064		794
Unpaid Principal Balance	1,064		1,064		1,144
Specific Allowance	0		0		0
Average Investment in Impaired Loans	1,493	684	1,500	691
Interest Income Recognized	17	6	26	14
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	981		981		1,067
Unpaid Principal Balance	981		981		1,067
Specific Allowance	463		463		714
Average Investment in Impaired Loans	1,028	5,969	1,047	5,145
Interest Income Recognized	5	80	22	125
Loans with a specific valuation allowance | Commercial
Financing Receivable, Impaired [Line Items]
Recorded Balance	98		98		105
Unpaid Principal Balance	98		98		105
Specific Allowance	86		86		92
Average Investment in Impaired Loans	100	422	102	439
Interest Income Recognized	2	2	4	4
Loans with a specific valuation allowance | Commercial real estate
Financing Receivable, Impaired [Line Items]
Recorded Balance	883		883		962
Unpaid Principal Balance	883		883		962
Specific Allowance	377		377		622
Average Investment in Impaired Loans	928	5,547	945	4,706
Interest Income Recognized	3	78	18	121
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	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