Loans - Allowance for Loan Losses Disaggregated on the Basis of Impairment Methodology (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	$ 2,508		$ 1,680	$ 1,389
Loans collectively evaluated for impairment	104,099		97,862	96,897
Ending balance	106,607	$ 105,708	99,542	98,286	$ 95,156	$ 92,438
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	2,437		1,613	613
Loans collectively evaluated for impairment	66,288		57,579	55,059
Ending balance	68,725	64,713	59,192	55,672	57,054	52,790
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	71		67	776
Loans collectively evaluated for impairment	24,864		27,096	21,270
Ending balance	24,935	27,105	27,163	22,046	21,020	22,590
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	0		0	0
Loans collectively evaluated for impairment	4,702		5,178	4,659
Ending balance	4,702	4,907	5,178	4,659	4,533	5,230
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	0		0	0
Loans collectively evaluated for impairment	8,245		8,009	6,427
Ending balance	8,245	$ 8,983	8,009	6,427	$ 5,691	$ 5,010
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	0		0	0
Loans collectively evaluated for impairment	0		0	9,482
Ending balance	$ 0		$ 0	$ 9,482