Allowance for Loan Losses - Changes in the Allowance for Loan Losses and Loan Balances Outstanding (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Allowance for loan losses:
Beginning balance	$ 14,315	$ 16,767	$ 14,268	$ 16,528
Charge-offs	(305)	(2,332)	(890)	(2,984)
Recoveries	297	210	529	351
Provision	400	750	800	1,500
Ending Balance	14,707	15,395	14,707	15,395
Commercial and Agriculture [Member]
Allowance for loan losses:
Beginning balance	1,794	2,607	1,822	2,841
Charge-offs		(84)		(313)
Recoveries	12	37	31	95
Provision	(411)	(493)	(458)	(556)
Ending Balance	1,395	2,067	1,395	2,067
Commercial Real Estate Owner Occupied [Member]
Allowance for loan losses:
Beginning balance	2,608	3,829	2,580	3,263
Charge-offs		(1,422)	(198)	(1,469)
Recoveries	208	70	210	75
Provision	2,611	658	2,835	1,266
Ending Balance	5,427	3,135	5,427	3,135
Commercial Real Estate Non Owner Occupied [Member]
Allowance for loan losses:
Beginning balance	4,926	4,168	4,798	4,296
Charge-offs	(55)	(78)	(64)	(105)
Recoveries	25	12	90	24
Provision	(1,513)	751	(1,441)	638
Ending Balance	3,383	4,853	3,383	4,853
Residential Real Estate [Member]
Allowance for loan losses:
Beginning balance	3,666	5,050	3,747	5,224
Charge-offs	(213)	(737)	(541)	(1,054)
Recoveries	34	72	165	121
Provision	(17)	54	99	148
Ending Balance	3,470	4,439	3,470	4,439
Real Estate Construction [Member]
Allowance for loan losses:
Beginning balance	498	295	428	184
Recoveries	2	2	3	3
Provision	(66)	(10)	3	100
Ending Balance	434	287	434	287
Consumer and Other [Member]
Allowance for loan losses:
Beginning balance	186	239	196	214
Charge-offs	(37)	(11)	(87)	(43)
Recoveries	16	17	30	33
Provision	25	(49)	51	(8)
Ending Balance	190	196	190	196
Unallocated [Member]
Allowance for loan losses:
Beginning balance	637	579	697	506
Provision	(229)	(161)	(289)	(88)
Ending Balance	$ 408	$ 418	$ 408	$ 418