Loans - Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	$ 17,415	$ 15,500	$ 16,234	$ 14,060
Charge-offs	(675)	(590)	(2,155)	(3,342)
Recoveries	65	1,465	206	1,612
Provision (benefit) for loan losses	1,038	846	3,558	4,891
Allowances for loan losses, Ending Balance	17,843	17,221	17,843	17,221
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	8,096	5,338	8,212	4,940
Charge-offs	(60)	(169)	(379)	(253)
Recoveries	0	0	1	7
Provision (benefit) for loan losses	690	384	892	859
Allowances for loan losses, Ending Balance	8,726	5,553	8,726	5,553
Commercial Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	4,581	5,896	3,536	4,697
Charge-offs	(92)	(4)	(142)	(1,534)
Recoveries	0	1,424	10	1,427
Provision (benefit) for loan losses	(291)	(275)	794	2,451
Allowances for loan losses, Ending Balance	4,198	7,041	4,198	7,041
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	2,467	2,508	2,450	2,466
Charge-offs	(17)	(57)	(215)	(398)
Recoveries	18	1	37	5
Provision (benefit) for loan losses	93	189	289	568
Allowances for loan losses, Ending Balance	2,561	2,641	2,561	2,641
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	1,996	1,555	1,763	1,699
Charge-offs	(415)	(269)	(1,183)	(946)
Recoveries	25	21	78	95
Provision (benefit) for loan losses	467	454	1,415	913
Allowances for loan losses, Ending Balance	2,073	1,761	2,073	1,761
Credit Cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	88	55	66	83
Charge-offs	(16)	(19)	(39)	(48)
Recoveries	4	3	7	13
Provision (benefit) for loan losses	3	18	45	9
Allowances for loan losses, Ending Balance	79	57	79	57
Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowances for loan losses, Beginning Balance	187	148	207	175
Charge-offs	(75)	(72)	(197)	(163)
Recoveries	18	16	73	65
Provision (benefit) for loan losses	76	76	123	91
Allowances for loan losses, Ending Balance	$ 206	$ 168	$ 206	$ 168