Allowance for Credit Losses and Allowance for Unfunded Commitments and Letters of Credit (Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	$ 142,988	$ 151,546	$ 142,988	$ 151,546	$ 148,294	$ 149,140	$ 122,074		$ 83,968
Financing Receivable, Allowance for Credit Loss, Writeoff	(1,940)	(5,640)	(5,406)	(12,429)
Financing Receivable, Allowance for Credit Loss, Recovery	2,134	1,612	5,554	3,375
Provision (recapture) for credit losses	(5,500)	33,500	(6,300)	75,000
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	53,250	50,233	53,250	50,233	57,050	68,934	37,122		20,340
Financing Receivable, Allowance for Credit Loss, Writeoff	(316)	0	(316)	(101)
Financing Receivable, Allowance for Credit Loss, Recovery	16	13	52	27
Provision (recapture) for credit losses	(3,500)	13,098	(15,420)	22,434
Commercial Business [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	57,554	53,186	57,554	53,186	58,405	45,250	45,570		30,292
Financing Receivable, Allowance for Credit Loss, Writeoff	(971)	(5,442)	(4,310)	(7,126)
Financing Receivable, Allowance for Credit Loss, Recovery	874	811	4,088	1,671
Provision (recapture) for credit losses	(754)	12,247	12,526	27,587
Agriculture [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	7,920	14,868	7,920	14,868	9,487	9,052	11,085		15,835
Financing Receivable, Allowance for Credit Loss, Writeoff	(122)	0	(122)	(4,726)
Financing Receivable, Allowance for Credit Loss, Recovery	5	1	17	42
Provision (recapture) for credit losses	(1,450)	3,782	(1,027)	13,042
Construction [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	6,559	7,953	6,559	7,953	6,551	7,636	8,845		8,571
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	521	235	567	677
Provision (recapture) for credit losses	(513)	(1,127)	(1,644)	455
One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	16,519	23,711	16,519	23,711	15,638	16,875	17,659		7,435
Financing Receivable, Allowance for Credit Loss, Writeoff	(146)	0	(146)	(10)
Financing Receivable, Allowance for Credit Loss, Recovery	503	422	554	704
Provision (recapture) for credit losses	524	5,630	(764)	11,345
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	1,186	1,595	1,186	1,595	$ 1,163	$ 1,393	1,644		883
Financing Receivable, Allowance for Credit Loss, Writeoff	(385)	(198)	(512)	(466)
Financing Receivable, Allowance for Credit Loss, Recovery	215	130	276	254
Provision (recapture) for credit losses	$ 193	19	$ 29	146
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss		0		0			$ 149		$ 612
Financing Receivable, Allowance for Credit Loss, Writeoff		0		0
Financing Receivable, Allowance for Credit Loss, Recovery		0		0
Provision (recapture) for credit losses		$ (149)		$ (9)
Accounting Standards Update 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								$ 1,632
Accounting Standards Update 2016-13 [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								7,533
Accounting Standards Update 2016-13 [Member] | Commercial Business [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								762
Accounting Standards Update 2016-13 [Member] | Agriculture [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								(9,325)
Accounting Standards Update 2016-13 [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								(1,750)
Accounting Standards Update 2016-13 [Member] | One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								4,237
Accounting Standards Update 2016-13 [Member] | Consumer Loan [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								778
Accounting Standards Update 2016-13 [Member] | Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Change in allowance for credit losses due to adoption of new ASU								$ (603)