Loans and Allowance for Loan and Lease Losses - Allowance for Loan Losses and Recorded Investment in Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Balance at beginning of quarter	$ 3,903	$ 3,993
Provision (credit) for losses	105us-gaap_ProvisionForLoanAndLeaseLosses	150us-gaap_ProvisionForLoanAndLeaseLosses
Charge-offs	(38)	(57)
Recoveries	14	14
Balance at end of quarter	3,984	4,100
Ending allowance balance: Individually evaluated for impairment	547		497
Ending allowance balance: Collectively evaluated for impairment	3,437		3,406
Total	3,984	4,100
Ending loan balance: Individually evaluated for impairment	10,848		10,839
Ending loan balance: Collectively evaluated for impairment	313,875		310,186
Total	324,723		321,025
Commercial Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of quarter	1,059	1,165
Provision (credit) for losses	74	108
Balance at end of quarter	1,133	1,273
Ending allowance balance: Collectively evaluated for impairment	1,133		1,059
Total	1,133	1,273
Ending loan balance: Individually evaluated for impairment	4,263		4,263
Ending loan balance: Collectively evaluated for impairment	109,868		107,192
Total	114,131		111,455
Residential Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of quarter	1,934	1,743
Provision (credit) for losses	69	1
Charge-offs	(25)
Recoveries	5	3
Balance at end of quarter	1,983	1,747
Ending allowance balance: Individually evaluated for impairment	365		319
Ending allowance balance: Collectively evaluated for impairment	1,618		1,615
Total	1,983	1,747
Ending loan balance: Individually evaluated for impairment	4,059		3,967
Ending loan balance: Collectively evaluated for impairment	156,921		159,872
Total	160,980		163,839
Construction Real Estate Loans [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of quarter	156	356
Provision (credit) for losses	68	15
Charge-offs		(40)
Recoveries	1	1
Balance at end of quarter	225	332
Ending allowance balance: Collectively evaluated for impairment	225		156
Total	225	332
Ending loan balance: Individually evaluated for impairment	1,975		2,004
Ending loan balance: Collectively evaluated for impairment	16,419		11,566
Total	18,394		13,570
Commercial Loans and Leases [Member]
Financing Receivable, Impaired [Line Items]
Balance at beginning of quarter	637	623
Provision (credit) for losses	(128)	2
Charge-offs		(1)
Recoveries	3	5
Balance at end of quarter	512	629
Ending allowance balance: Individually evaluated for impairment	154		166
Ending allowance balance: Collectively evaluated for impairment	358		471
Total	512	629
Ending loan balance: Individually evaluated for impairment	495		516
Ending loan balance: Collectively evaluated for impairment	26,855		28,842
Total	27,350		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 quarter	117	106
Provision (credit) for losses	22	24
Charge-offs	(13)	(16)
Recoveries	5	5
Balance at end of quarter	131	119
Ending allowance balance: Individually evaluated for impairment	28		12
Ending allowance balance: Collectively evaluated for impairment	103		105
Total	131	119
Ending loan balance: Individually evaluated for impairment	56		89
Ending loan balance: Collectively evaluated for impairment	1,917		1,929
Total	$ 1,973		$ 2,018

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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