Allowance for Loan Losses - Allowance Related to Unallocated Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Allowance for loan losses:
Beginning balance	$ 16,528	$ 19,742
Charge-offs	(652)	(881)
Recoveries	141	349
Provision	750	500
Ending Balance	16,767	19,710
Individually evaluated for impairment	3,034		2,509
Collectively evaluated for impairment	13,733		14,019
Ending Balance	16,767	19,710
Loan balances outstanding:
Individually evaluated for impairment	19,279		18,057
Collectively evaluated for impairment	838,089		843,184
Ending Balance	857,368		861,241
Commercial and Agriculture [Member]
Allowance for loan losses:
Beginning balance	2,841	2,811
Charge-offs	(229)
Recoveries	58	41
Provision	(63)	85
Ending Balance	2,607	2,937
Individually evaluated for impairment	1,172		1,262
Collectively evaluated for impairment	1,435		1,579
Ending Balance	2,607	2,937
Loan balances outstanding:
Individually evaluated for impairment	4,751		3,869
Collectively evaluated for impairment	98,614		112,006
Ending Balance	103,365		115,875
Commercial Real Estate [Member]
Allowance for loan losses:
Beginning balance	7,559	10,139
Charge-offs	(74)	(312)
Recoveries	17	90
Provision	495	7
Ending Balance	7,997	9,924
Individually evaluated for impairment	1,092		445
Collectively evaluated for impairment	6,905		7,114
Ending Balance	7,997	9,924
Loan balances outstanding:
Individually evaluated for impairment	10,729		10,175
Collectively evaluated for impairment	430,095		433,671
Ending Balance	440,824		443,846
Residential Real Estate [Member]
Allowance for loan losses:
Beginning balance	5,224	5,780
Charge-offs	(317)	(487)
Recoveries	49	156
Provision	94	(35)
Ending Balance	5,050	5,414
Individually evaluated for impairment	770		802
Collectively evaluated for impairment	4,280		4,422
Ending Balance	5,050	5,414
Loan balances outstanding:
Individually evaluated for impairment	3,792		4,005
Collectively evaluated for impairment	245,500		246,686
Ending Balance	249,292		250,691
Real Estate Construction [Member]
Allowance for loan losses:
Beginning balance	184	349
Charge-offs
Recoveries	1	52
Provision	110	(87)
Ending Balance	295	314
Individually evaluated for impairment
Collectively evaluated for impairment	295		184
Ending Balance	295	314
Loan balances outstanding:
Individually evaluated for impairment
Collectively evaluated for impairment	52,788		39,964
Ending Balance	52,788		39,964
Unallocated [Member]
Allowance for loan losses:
Beginning balance	506	417
Charge-offs
Recoveries
Provision	73	479
Ending Balance	579	896
Individually evaluated for impairment
Collectively evaluated for impairment	579		506
Ending Balance	579	896
Loan balances outstanding:
Individually evaluated for impairment	7		8
Collectively evaluated for impairment	11,092		10,857
Ending Balance	11,099		10,865
Consumer and Other [Member]
Allowance for loan losses:
Beginning balance	214	246
Charge-offs	(32)	(82)
Recoveries	16	10
Provision	41	51
Ending Balance	239	225
Individually evaluated for impairment
Collectively evaluated for impairment	239		214
Ending Balance	$ 239	$ 225