Allowance for Credit Losses and Allowance for Unfunded Commitments and Letters of Credit (Allowance for Credit Losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	$ 142,785	$ 156,968	$ 142,785	$ 156,968	$ 142,988	$ 149,140	$ 151,546		$ 83,968
Financing Receivable, Allowance for Credit Loss, Writeoff	(1,479)	(4,582)	(6,885)	(17,011)
Financing Receivable, Allowance for Credit Loss, Recovery	1,276	2,604	6,830	5,979
Provision (recapture) for credit losses	0	7,400	(6,300)	82,400
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	51,752	61,324	51,752	61,324	53,250	68,934	50,233		20,340
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0	(316)	(101)
Financing Receivable, Allowance for Credit Loss, Recovery	518	65	570	92
Provision (recapture) for credit losses	(2,016)	11,026	(17,436)	33,460
Commercial Business [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	55,561	50,572	55,561	50,572	57,554	45,250	53,186		30,292
Financing Receivable, Allowance for Credit Loss, Writeoff	(1,183)	(3,164)	(5,493)	(10,290)
Financing Receivable, Allowance for Credit Loss, Recovery	328	1,124	4,416	2,795
Provision (recapture) for credit losses	(1,138)	(574)	11,388	27,013
Agriculture [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	8,965	12,461	8,965	12,461	7,920	9,052	14,868		15,835
Financing Receivable, Allowance for Credit Loss, Writeoff	0	(1,269)	(122)	(5,995)
Financing Receivable, Allowance for Credit Loss, Recovery	6	27	23	69
Provision (recapture) for credit losses	1,039	(1,165)	12	11,877
Construction [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	6,367	8,963	6,367	8,963	6,559	7,636	7,953		8,571
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	8	11	575	688
Provision (recapture) for credit losses	(200)	999	(1,844)	1,454
One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	18,855	22,107	18,855	22,107	16,519	16,875	23,711		7,435
Financing Receivable, Allowance for Credit Loss, Writeoff	0	(16)	(146)	(26)
Financing Receivable, Allowance for Credit Loss, Recovery	203	1,301	757	2,005
Provision (recapture) for credit losses	2,133	(2,889)	1,369	8,456
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	1,285	1,541	1,285	1,541	$ 1,186	$ 1,393	$ 1,595		883
Financing Receivable, Allowance for Credit Loss, Writeoff	(296)	(133)	(808)	(599)
Financing Receivable, Allowance for Credit Loss, Recovery	213	76	489	330
Provision (recapture) for credit losses	$ 182	3	$ 211	149
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss		$ 0		0					$ 612
Financing Receivable, Allowance for Credit Loss, Writeoff				0
Financing Receivable, Allowance for Credit Loss, Recovery				0
Provision (recapture) for credit losses				$ (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)