Loans and Allowance for Loan Losses - Allowance for Loan Losses Activity by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	$ 42,913	$ 59,868	$ 49,006	$ 24,797
Loans charged-off	(940)	(718)	(2,262)	(2,259)
Recoveries of loans charged-off	437	361	1,525	1,248
Net loans (charged-off) recovered	(503)	(357)	(737)	(1,011)
Provision for (reversal of) loan losses(1)	(4,388)	(4,401)	(10,247)	26,021	[1]
Balance at end of period	38,022	55,110	38,022	55,110
Construction Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	8,018	8,500	6,490	3,539
Loans charged-off	0	(6)	0	(39)
Recoveries of loans charged-off	1	0	2	11
Net loans (charged-off) recovered	1	(6)	2	(28)
Provision for (reversal of) loan losses(1)	(3,036)	(2,868)	(1,509)	(838)	[1]
Balance at end of period	4,983	5,626	4,983	5,626
1-4 Family Residential Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	2,520	2,702	2,270	3,833
Loans charged-off	(35)	(18)	(136)	(74)
Recoveries of loans charged-off	4	9	71	29
Net loans (charged-off) recovered	(31)	(9)	(65)	(45)
Provision for (reversal of) loan losses(1)	(543)	(58)	(259)	300	[1]
Balance at end of period	1,946	2,635	1,946	2,635
Commercial Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	28,930	43,785	35,709	9,572
Loans charged-off	0	(12)	0	(33)
Recoveries of loans charged-off	12	13	13	94
Net loans (charged-off) recovered	12	1	13	61
Provision for (reversal of) loan losses(1)	(684)	(2,001)	(7,464)	24,089	[1]
Balance at end of period	28,258	41,785	28,258	41,785
Commercial loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	3,097	4,221	4,107	6,351
Loans charged-off	(508)	(279)	(943)	(800)
Recoveries of loans charged-off	74	61	535	191
Net loans (charged-off) recovered	(434)	(218)	(408)	(609)
Provision for (reversal of) loan losses(1)	(103)	489	(1,139)	2,304	[1]
Balance at end of period	2,560	4,492	2,560	4,492
Municipal loans
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	47	47	46	570
Loans charged-off	0	0	0	0
Recoveries of loans charged-off	0	0	0	0
Net loans (charged-off) recovered	0	0	0	0
Provision for (reversal of) loan losses(1)	(1)	(1)	0	(2)	[1]
Balance at end of period	46	46	46	46
Loans to individuals
Allowances for Loan Losses [Roll Forward]
Balance at beginning of period	301	613	384	932
Loans charged-off	(397)	(403)	(1,183)	(1,313)
Recoveries of loans charged-off	346	278	904	923
Net loans (charged-off) recovered	(51)	(125)	(279)	(390)
Provision for (reversal of) loan losses(1)	(21)	38	124	168	[1]
Balance at end of period	$ 229	$ 526	$ 229	526
Impact of CECL adoption
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				5,072
Impact of CECL adoption - purchased loans with credit deterioration				231
Impact of CECL adoption | Construction Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				2,968
Impact of CECL adoption - purchased loans with credit deterioration				(15)
Impact of CECL adoption | 1-4 Family Residential Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				(1,447)
Impact of CECL adoption - purchased loans with credit deterioration				(6)
Impact of CECL adoption | Commercial Real Estate Loans
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				7,730
Impact of CECL adoption - purchased loans with credit deterioration				333
Impact of CECL adoption | Commercial loans
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				(3,532)
Impact of CECL adoption - purchased loans with credit deterioration				(22)
Impact of CECL adoption | Municipal loans
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				(522)
Impact of CECL adoption - purchased loans with credit deterioration				0
Impact of CECL adoption | Loans to individuals
Allowances for Loan Losses [Roll Forward]
Impact of CECL adoption - cumulative effect adjustment				(125)
Impact of CECL adoption - purchased loans with credit deterioration				$ (59)

[1] The increase in the provision for credit losses during the nine months ended September 30, 2020 was primarily due to the economic impact of COVID-19 on macroeconomic factors used in the CECL model.