Allowance for Loan Losses - Aging of Past Due Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	$ 1,468	$ 3,251
Non Accrual	3,996	2,014	$ 1,313
Accruing Greater Than 90 Days	90	0	$ 0
Total Past Due	5,554	5,265
Current Loans	2,990,275	2,420,854
Total loans, net	2,995,829	2,426,119
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current Loans	10,909	8,992
Total loans, net	10,909	8,992
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	56	227
Non Accrual	297	400
Accruing Greater Than 90 Days	90
Total Past Due	443	627
Current Loans	1,313,802	811,790
Total loans, net	1,314,245	812,417
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current Loans	137,607	120,455
Total loans, net	137,607	120,455
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due		840
Non Accrual	2,881	492
Total Past Due	2,881	1,332
Current Loans	786,955	784,770
Total loans, net	789,836	786,102
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	390	1,563
Non Accrual	527	683
Total Past Due	917	2,246
Current Loans	447,519	369,651
Total loans, net	448,436	371,897
Consumer and overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	21	18
Non Accrual	1	4
Total Past Due	22	22
Current Loans	20,417	21,871
Total loans, net	20,439	21,893
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	1,001	603
Non Accrual	290	435
Total Past Due	1,291	1,038
Current Loans	273,066	303,325
Total loans, net	$ 274,357	$ 304,363