Loans - Aging of Recorded Investment in Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 5,456	$ 6,019
60-89 Days Past Due	3,064	2,447
Greater Than 90 Days Past Due	11,440	11,766
Total Past Due	19,960	20,232
Loans Not Past Due	1,292,419	1,279,027
Total	1,312,379	1,299,259
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	442	211
60-89 Days Past Due	1,708	542
Greater Than 90 Days Past Due	1,643	855
Total Past Due	3,793	1,608
Loans Not Past Due	418,606	426,107
Total	422,399	427,715
Commercial Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,213	1,258
60-89 Days Past Due	129	713
Greater Than 90 Days Past Due	4,553	7,236
Total Past Due	5,895	9,207
Loans Not Past Due	336,153	334,258
Total	342,048	343,465
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	3,648	4,216
60-89 Days Past Due	1,074	114
Greater Than 90 Days Past Due	4,940	2,539
Total Past Due	9,662	6,869
Loans Not Past Due	467,524	452,245
Total	477,186	459,114
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	153	334
60-89 Days Past Due	50	1,049
Greater Than 90 Days Past Due	251	1,112
Total Past Due	454	2,495
Loans Not Past Due	64,860	60,996
Total	65,314	63,491
Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	103	29
Greater Than 90 Days Past Due	53	24
Total Past Due	156	53
Loans Not Past Due	4,959	5,012
Total	5,115	5,065
Overdrafts [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
Greater Than 90 Days Past Due	0	0
Total Past Due	0	0
Loans Not Past Due	317	409
Total	$ 317	$ 409