Loans - Aging of Recorded Investment in Past Due Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 15,270	$ 13,352
Loans Not Past Due	1,644,321	1,569,002
Total	1,659,591	1,582,354
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,361	3,188
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,183	1,522
Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,726	8,642
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,788	1,451
Loans Not Past Due	488,050	473,913
Total	490,838	475,364
Commercial, Industrial, and Agricultural [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,000	131
Commercial, Industrial, and Agricultural [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	775	622
Commercial, Industrial, and Agricultural [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,013	698
Commercial Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,796	4,001
Loans Not Past Due	490,823	444,178
Total	494,619	448,179
Commercial Mortgages [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	477	7
Commercial Mortgages [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	343
Commercial Mortgages [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,319	3,651
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,900	6,213
Loans Not Past Due	584,879	568,012
Total	591,779	574,225
Residential Real Estate [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,480	2,834
Residential Real Estate [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,130	378
Residential Real Estate [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,290	3,001
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,691	1,687
Loans Not Past Due	74,928	76,658
Total	76,619	78,345
Consumer [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	365	216
Consumer [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	238	179
Consumer [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,088	1,292
Credit Cards [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	95	0
Loans Not Past Due	5,234	5,201
Total	5,329	5,201
Credit Cards [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	39	0
Credit Cards [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	40	0
Credit Cards [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16	0
Overdrafts [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Loans Not Past Due	407	1,040
Total	407	1,040
Overdrafts [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Overdrafts [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Overdrafts [Member] | Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 0