Loans and Allowance for Loan Losses - Loans by Portfolio Segment (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
Loans and Leases Receivable Disclosure [Abstract]
Total loans	$ 3,789,975			$ 3,568,204
Less: Allowance for loan losses	55,110	$ 59,868	$ 24,797	24,797	$ 25,129	$ 24,705	$ 27,019
Total loans	3,734,865			3,543,407
Construction Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total loans	610,394			644,948
Less: Allowance for loan losses	5,626	8,500	3,539	3,539	3,576	3,599	3,597
1-4 Family Residential Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total loans	738,343			787,562
Less: Allowance for loan losses	2,635	2,702	3,833	3,833	3,556	3,522	3,844
Commercial Real Estate Loans
Loans and Leases Receivable Disclosure [Abstract]
Total loans	1,327,233			1,250,208
Less: Allowance for loan losses	41,785	43,785	9,572	9,572	10,582	10,534	13,968
Commercial loans
Loans and Leases Receivable Disclosure [Abstract]
Total loans	629,170			401,521
Less: Allowance for loan losses	4,492	4,221	6,351	6,351	5,852	5,546	3,974
Municipal loans
Loans and Leases Receivable Disclosure [Abstract]
Total loans	387,286			383,960
Less: Allowance for loan losses	46	47	570	570	547	530	525
Loans to individuals
Loans and Leases Receivable Disclosure [Abstract]
Total loans	97,549			100,005
Less: Allowance for loan losses	$ 526	$ 613	$ 932	$ 932	$ 1,016	$ 974	$ 1,111