Summary of Significant Accounting Policies - Impact of Adoption (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Debt securities, available-for-sale, allowance for credit loss	$ 692
Allowance for credit losses, loans and lease	91,870	$ 86,217	$ 35,331	$ 35,331	$ 33,662	$ 32,600	$ 29,364
Reserve for unfunded commitments			420
Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			12,922
Reserve for unfunded commitments			1,145
Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			48,253
Reserve for unfunded commitments			1,565
Commercial Financial And Agricultural [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	14,547	16,736	8,759	8,759	9,250	9,129	7,983
Commercial Financial And Agricultural [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			5,284
Commercial Financial And Agricultural [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			14,043
Real-Estate Commercial [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	58,152	50,671	15,750	15,750
Real-Estate Commercial [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			6,208
Real-Estate Commercial [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			21,958
Real-Estate Construction [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	4,485	4,130	2,446	2,446
Real-Estate Construction [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			29
Real-Estate Construction [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			2,475
Real Estate Residential Secured For Business Purpose [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	8,366	8,180	2,622	2,622	2,685	2,478	2,236
Real Estate Residential Secured For Business Purpose [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			2,502
Real Estate Residential Secured For Business Purpose [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			5,124
Real Estate Residential Secured For Personal Purpose [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	2,716	2,669	2,713	2,713
Real Estate Residential Secured For Personal Purpose [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			(706)
Real Estate Residential Secured For Personal Purpose [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			2,007
Real Estate Home Equity Secured For Personal Purpose [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	1,279	1,071	1,076	1,076
Real Estate Home Equity Secured For Personal Purpose [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			(364)
Real Estate Home Equity Secured For Personal Purpose [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			712
Loans to Individuals [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	549	771	470	470	475	481	484
Loans to Individuals [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			104
Loans to Individuals [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			574
Lease Financings [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	1,626	1,839	1,311	1,311	1,234	1,241	1,288
Lease Financings [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			(135)
Lease Financings [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			1,176
Unallocated [Member]
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease	150	150	184	184	$ 585	$ 275	$ 271
Unallocated [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			0
Unallocated [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Allowance for credit losses, loans and lease			184
Corporate Bonds [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt securities, available-for-sale, allowance for credit loss	$ 692	$ 855	0	$ 0
Corporate Bonds [Member] | Cumulative Effect, Period Of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Debt securities, available-for-sale, allowance for credit loss			300
Corporate Bonds [Member] | Cumulative Effect, Period Of Adoption, Adjusted Balance
Summary Of Significant Accounting Policies [Line Items]
Debt securities, available-for-sale, allowance for credit loss			$ 300