Loans and Allowance for Loan Losses - Allowance for Credit Losses Based on Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	$ 38,381	$ 26,359	$ 26,911	$ 26,189	$ 26,189
Provision for credit loss expense	3,883	2,658	15,500	3,696	6,433
Loans charged off	556	2,460	2,942	3,570	6,326
Recoveries collected	207	184	774	426	615
Ending balance	41,915	26,741	41,915	26,741	26,911
Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			1,672
Ending balance					1,672
Construction and Land Development \| Real Estate Loan
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	2,358	739	1,146	561	561
Provision for credit loss expense	(139)	759	1,186	937	585
Loans charged off	13	0	13	0	0
Recoveries collected	0	0	0	0	0
Ending balance	2,206	1,498	2,206	1,498	1,146
Construction and Land Development \| Real Estate Loan \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			(113)
Ending balance					(113)
Agricultural \| Real Estate Loan
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	1,634	1,284	1,093	1,246	1,246
Provision for credit loss expense	32	(134)	343	(96)	(153)
Loans charged off	0	0	0	0	0
Recoveries collected	0	0	0	0	0
Ending balance	1,666	1,150	1,666	1,150	1,093
Agricultural \| Real Estate Loan \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			230
Ending balance					230
Residential Properties \| Real Estate Loan \| 1-4 Family
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	2,486	1,649	1,386	1,504	1,504
Provision for credit loss expense	(71)	618	335	944	1,268
Loans charged off	48	514	313	711	1,478
Recoveries collected	24	59	227	75	92
Ending balance	2,391	1,812	2,391	1,812	1,386
Residential Properties \| Real Estate Loan \| 1-4 Family \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			756
Ending balance					756
Commercial \| Real Estate Loan
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	16,272	10,796	11,198	11,102	11,102
Provision for credit loss expense	2,463	229	7,542	83	1,827
Loans charged off	0	866	551	1,027	1,743
Recoveries collected	73	5	78	6	12
Ending balance	18,808	10,164	18,808	10,164	11,198
Commercial \| Real Estate Loan \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			541
Ending balance					541
Agricultural Loans
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	1,323	1,672	1,386	951	951
Provision for credit loss expense	(89)	(87)	211	642	459
Loans charged off	0	15	0	23	24
Recoveries collected	0	0	0	0	0
Ending balance	1,234	1,570	1,234	1,570	1,386
Agricultural Loans \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			(363)
Ending balance					(363)
Commercial And Industrial Portfolio Segment
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	12,360	9,130	9,273	9,893	9,893
Provision for credit loss expense	1,352	791	5,453	246	1,053
Loans charged off	368	724	1,651	982	1,828
Recoveries collected	28	47	142	87	155
Ending balance	13,372	9,244	13,372	9,244	9,273
Commercial And Industrial Portfolio Segment \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			155
Ending balance					155
Consumer Loans
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	1,948	1,089	1,429	932	932
Provision for credit loss expense	335	482	430	940	1,394
Loans charged off	127	341	414	827	1,253
Recoveries collected	82	73	327	258	356
Ending balance	$ 2,238	$ 1,303	2,238	$ 1,303	1,429
Consumer Loans \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance			$ 466
Ending balance					$ 466

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of increase (decrease) in allowance for credit loss on financing receivable.

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