Loans and Allowance for Loan and Lease Losses - Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Average Investment In Impaired Loans	$ 8,188	$ 9,697	$ 8,181	$ 9,177	$ 8,332
Loans without a specific valuation allowance, Interest Income Recognized	74	94	147	181	306
Loans without a specific valuation allowance, Recorded Balance	8,285	8,286	8,285	8,286	9,023
All Impaired Loans, Recorded Balance	14,009	14,267	14,009	14,267	10,839
Loans without a specific valuation allowance, Unpaid Principal Balance	9,092	9,892	9,092	9,892	9,768
All Impaired Loans, Unpaid Principal Balance	14,890	15,990	14,890	15,990	11,692
Loans with a specific valuation allowance, Recorded Balance	5,724	5,981	5,724	5,981	1,816
Loans with a specific valuation allowance, Unpaid Principal Balance	5,798	6,098	5,798	6,098	1,924
All Impaired Loans, Specific Allowance	886	743	886	743	497
Loans with a specific valuation allowance, Average Investment In Impaired Loans	2,459	5,739	2,460	5,866	5,958
All Impaired Loans, Average Investment in Impaired Loans	10,647	15,436	10,641	15,043	14,290
Loans with a specific valuation allowance, Interest Income Recognized	4	46	8	93	155
All Impaired Loans, Interest Income Recognized	78	140	155	274	461
Commercial Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Average Investment In Impaired Loans	3,451	4,471	3,451	4,435	4,025
Loans without a specific valuation allowance, Interest Income Recognized	43	59	86	110	176
Loans without a specific valuation allowance, Recorded Balance	3,451	4,339	3,451	4,339	4,263
Loans without a specific valuation allowance, Unpaid Principal Balance	3,929	4,817	3,929	4,817	4,742
Loans with a specific valuation allowance, Recorded Balance	812		812
Loans with a specific valuation allowance, Unpaid Principal Balance	812		812
All Impaired Loans, Specific Allowance	70		70
Loans with a specific valuation allowance, Average Investment In Impaired Loans	812		812		481
Loans with a specific valuation allowance, Interest Income Recognized					22
Residential Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Average Investment In Impaired Loans	2,706	3,273	2,684	3,014	2,342
Loans without a specific valuation allowance, Interest Income Recognized	14	17	28	35	58
Loans without a specific valuation allowance, Recorded Balance	2,819	2,655	2,819	2,655	2,686
Loans without a specific valuation allowance, Unpaid Principal Balance	3,120	2,920	3,120	2,920	2,923
Loans with a specific valuation allowance, Recorded Balance	4,456	2,589	4,456	2,589	1,281
Loans with a specific valuation allowance, Unpaid Principal Balance	4,467	2,662	4,467	2,662	1,340
All Impaired Loans, Specific Allowance	649	381	649	381	319
Loans with a specific valuation allowance, Average Investment In Impaired Loans	1,180	2,609	1,161	2,602	2,806
Loans with a specific valuation allowance, Interest Income Recognized	4	21	8	42	78
Construction Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Average Investment In Impaired Loans	1,962	1,389	1,976	1,329	1,744
Loans without a specific valuation allowance, Interest Income Recognized	17	18	33	36	72
Loans without a specific valuation allowance, Recorded Balance	1,948	1,222	1,948	1,222	2,004
Loans without a specific valuation allowance, Unpaid Principal Balance	1,948	2,057	1,948	2,057	2,004
Loans with a specific valuation allowance, Recorded Balance		3,149		3,149
Loans with a specific valuation allowance, Unpaid Principal Balance		3,149		3,149
All Impaired Loans, Specific Allowance		245		245
Loans with a specific valuation allowance, Average Investment In Impaired Loans		2,901		3,025	2,368
Loans with a specific valuation allowance, Interest Income Recognized		25		51	55
Commercial Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Loans without a specific valuation allowance, Average Investment In Impaired Loans	69	564	70	399	221
Loans without a specific valuation allowance, Recorded Balance	67	70	67	70	70
Loans without a specific valuation allowance, Unpaid Principal Balance	95	98	95	98	99
Loans with a specific valuation allowance, Recorded Balance	368	148	368	148	446
Loans with a specific valuation allowance, Unpaid Principal Balance	431	192	431	192	495
All Impaired Loans, Specific Allowance	139	109	139	109	166
Loans with a specific valuation allowance, Average Investment In Impaired Loans	396	163	415	161	222
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Loans with a specific valuation allowance, Recorded Balance	88	95	88	95	89
Loans with a specific valuation allowance, Unpaid Principal Balance	88	95	88	95	89
All Impaired Loans, Specific Allowance	28	8	28	8	12
Loans with a specific valuation allowance, Average Investment In Impaired Loans	$ 71	$ 66	$ 72	$ 78	$ 81