Loans and Allowance for Loan and Lease Losses - Allowance for Loan Losses and Recorded Investment in 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
Financing Receivable, Impaired [Line Items]
Balance at beginning of period	$ 3,984	$ 4,100	$ 3,903	$ 3,993
Provision (credit) for losses		150	105	300
Charge-offs	(121)	(263)	(159)	(320)
Recoveries	41	17	55	31
Balance at end of period	3,904	4,004	3,904	4,004
Ending allowance balance: Individually evaluated for impairment			886		$ 497
Ending allowance balance: Collectively evaluated for impairment			3,018		3,406
Total	3,984	4,100	3,904	4,004	3,903
Ending loan balance: Individually evaluated for impairment			14,009		10,839
Ending loan balance: Collectively evaluated for impairment			318,533		310,186
Total			332,542		321,025
Commercial Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of period	1,133	1,273	1,059	1,165
Provision (credit) for losses	(46)	73	28	181
Charge-offs		(101)		(101)
Recoveries		3		3
Balance at end of period	1,087	1,248	1,087	1,248
Ending allowance balance: Individually evaluated for impairment			70
Ending allowance balance: Collectively evaluated for impairment			1,017		1,059
Total	1,133	1,273	1,087	1,248	1,059
Ending loan balance: Individually evaluated for impairment			4,263		4,263
Ending loan balance: Collectively evaluated for impairment			112,209		107,192
Total			116,472		111,455
Residential Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of period	1,983	1,747	1,934	1,743
Provision (credit) for losses	70	13	139	14
Charge-offs	(58)	(80)	(83)	(80)
Recoveries	26	3	31	6
Balance at end of period	2,021	1,683	2,021	1,683
Ending allowance balance: Individually evaluated for impairment			649		319
Ending allowance balance: Collectively evaluated for impairment			1,372		1,615
Total	1,983	1,747	2,021	1,683	1,934
Ending loan balance: Individually evaluated for impairment			7,275		3,967
Ending loan balance: Collectively evaluated for impairment			156,192		159,872
Total			163,467		163,839
Construction Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of period	225	332	156	356
Provision (credit) for losses	(23)	65	45	80
Charge-offs		(6)		(46)
Recoveries		1	1	2
Balance at end of period	202	392	202	392
Ending allowance balance: Collectively evaluated for impairment			202		156
Total	225	332	202	392	156
Ending loan balance: Individually evaluated for impairment			1,948		2,004
Ending loan balance: Collectively evaluated for impairment			16,689		11,566
Total			18,637		13,570
Commercial Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of period	512	629	637	623
Provision (credit) for losses		(19)	(128)	(17)
Charge-offs	(48)	(58)	(48)	(59)
Recoveries	5	6	8	11
Balance at end of period	469	558	469	558
Ending allowance balance: Individually evaluated for impairment			139		166
Ending allowance balance: Collectively evaluated for impairment			330		471
Total	512	629	469	558	637
Ending loan balance: Individually evaluated for impairment			435		516
Ending loan balance: Collectively evaluated for impairment			29,761		28,842
Total			30,196		29,358
Municipal Loans [Member]
Financing Receivable, Impaired [Line Items]
Ending loan balance: Collectively evaluated for impairment			1,895		785
Total			1,895		785
Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of period	131	119	117	106
Provision (credit) for losses	(1)	18	21	42
Charge-offs	(15)	(18)	(28)	(34)
Recoveries	10	4	15	9
Balance at end of period	125	123	125	123
Ending allowance balance: Individually evaluated for impairment			28		12
Ending allowance balance: Collectively evaluated for impairment			97		105
Total	$ 131	$ 119	125	$ 123	117
Ending loan balance: Individually evaluated for impairment			88		89
Ending loan balance: Collectively evaluated for impairment			1,787		1,929
Total			$ 1,875		$ 2,018