Loans and Allowance for Credit Losses - Allowance for Credit Losses Based on Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	$ 41,910	$ 26,911	$ 26,911
Initial allowance on loans purchased with credit deterioration	2,074
Provision for credit loss expense	12,136	5,481	16,103
Loans charged off	968	1,423	3,844
Recoveries collected	266	235	1,068
Allowance for credit losses, Ending Balance	55,418	32,876	41,910
Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance		1,672	1,672
Construction and Land Development \| Real Estate Loan
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	1,666	1,146	1,146
Initial allowance on loans purchased with credit deterioration	261
Provision for credit loss expense	359	587	646
Loans charged off	0	0	13
Recoveries collected	0	0	0
Allowance for credit losses, Ending Balance	2,286	1,620	1,666
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)	(113)
Agricultural \| Real Estate Loan
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	1,084	1,093	1,093
Initial allowance on loans purchased with credit deterioration	44
Provision for credit loss expense	500	12	(239)
Loans charged off	0	0	0
Recoveries collected	0	0	0
Allowance for credit losses, Ending Balance	1,628	1,335	1,084
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	230
Residential Properties \| Real Estate Loan \| 1-4 Family
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	2,322	1,386	1,386
Initial allowance on loans purchased with credit deterioration	328
Provision for credit loss expense	617	(77)	274
Loans charged off	182	196	393
Recoveries collected	8	62	299
Allowance for credit losses, Ending Balance	3,093	1,931	2,322
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	756
Commercial \| Real Estate Loan
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	19,660	11,198	11,198
Initial allowance on loans purchased with credit deterioration	646
Provision for credit loss expense	5,902	1,961	8,581
Loans charged off	480	84	829
Recoveries collected	9	5	169
Allowance for credit losses, Ending Balance	25,737	13,621	19,660
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	541
Agricultural Loans
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	1,526	1,386	1,386
Initial allowance on loans purchased with credit deterioration	0
Provision for credit loss expense	(645)	41	503
Loans charged off	0	0	0
Recoveries collected	0	0	0
Allowance for credit losses, Ending Balance	881	1,064	1,526
Agricultural Loans \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance		(363)	(363)
Commercial and Industrial Loans
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	13,485	9,273	9,273
Initial allowance on loans purchased with credit deterioration	795
Provision for credit loss expense	4,674	2,815	5,869
Loans charged off	18	972	1,991
Recoveries collected	18	23	179
Allowance for credit losses, Ending Balance	18,954	11,294	13,485
Commercial and Industrial Loans \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance		155	155
Consumer Loans
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance	2,167	1,429	1,429
Initial allowance on loans purchased with credit deterioration	0
Provision for credit loss expense	729	142	469
Loans charged off	288	171	618
Recoveries collected	231	145	421
Allowance for credit losses, Ending Balance	$ 2,839	2,011	2,167
Consumer Loans \| Cumulative Change in Accounting Principal, Adjustment \| ASU 2016-13
Allowance for loan losses [Abstract]
Allowance for credit losses, Beginning Balance		$ 466	$ 466

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Amount of increase in allowance for credit loss on financing receivable purchased with credit deterioration.

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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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