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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	$ 151,546	$ 80,517	$ 151,546	$ 80,517	$ 122,074	$ 85,600	$ 83,968	$ 83,274	$ 83,369
Financing Receivable, Allowance for Credit Loss, Writeoff	(5,640)	(5,287)	(12,429)	(8,275)
Financing Receivable, Allowance for Credit Loss, Recovery	1,612	2,312	3,375	3,843
Provision for credit losses	33,500	218	75,000	1,580
Allowance on Individually Measured Loans	4,036	1,475	4,036	1,475
Allowance on Collectively Measured Loans	147,510	79,042	147,510	79,042
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	50,233	15,648	50,233	15,648	37,122	27,873	20,340	16,359	14,766
Financing Receivable, Allowance for Credit Loss, Writeoff	0	(564)	(101)	(1,242)
Financing Receivable, Allowance for Credit Loss, Recovery	13	556	27	1,070
Provision for credit losses	13,098	(703)	22,434	1,054
Allowance on Individually Measured Loans	0	44	0	44
Allowance on Collectively Measured Loans	50,233	15,604	50,233	15,604
Commercial Business [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	53,186	29,700	53,186	29,700	45,570	31,054	30,292	34,545	34,658
Financing Receivable, Allowance for Credit Loss, Writeoff	(5,442)	(4,316)	(7,126)	(5,822)
Financing Receivable, Allowance for Credit Loss, Recovery	811	492	1,671	1,019
Provision for credit losses	12,247	(1,021)	27,587	(155)
Allowance on Individually Measured Loans	3,208	691	3,208	691
Allowance on Collectively Measured Loans	49,978	29,009	49,978	29,009
Agriculture [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	14,868	12,671	14,868	12,671	11,085	6,510	15,835	10,690	9,589
Financing Receivable, Allowance for Credit Loss, Writeoff	0	(61)	(4,726)	(139)
Financing Receivable, Allowance for Credit Loss, Recovery	1	64	42	122
Provision for credit losses	3,782	1,978	13,042	3,099
Allowance on Individually Measured Loans	828	712	828	712
Allowance on Collectively Measured Loans	14,040	11,959	14,040	11,959
Construction [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	7,953	12,457	7,953	12,457	8,845	6,821	8,571	11,965	14,395
Financing Receivable, Allowance for Credit Loss, Writeoff	0	(20)	0	(215)
Financing Receivable, Allowance for Credit Loss, Recovery	235	691	677	774
Provision for credit losses	(1,127)	(179)	455	(2,497)
Allowance on Individually Measured Loans	0	0	0	0
Allowance on Collectively Measured Loans	7,953	12,457	7,953	12,457
One-to-Four Family Residential [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	23,711	7,619	23,711	7,619	17,659	11,672	7,435	8,311	8,024
Financing Receivable, Allowance for Credit Loss, Writeoff	0	(321)	(10)	(802)
Financing Receivable, Allowance for Credit Loss, Recovery	422	450	704	784
Provision for credit losses	5,630	(821)	11,345	(387)
Allowance on Individually Measured Loans	0	27	0	27
Allowance on Collectively Measured Loans	23,711	7,592	23,711	7,592
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	1,595	715	1,595	715	1,644	1,661	883	823	787
Financing Receivable, Allowance for Credit Loss, Writeoff	(198)	(5)	(466)	(55)
Financing Receivable, Allowance for Credit Loss, Recovery	130	59	254	74
Provision for credit losses	19	(162)	146	(91)
Allowance on Individually Measured Loans	0	1	0	1
Allowance on Collectively Measured Loans	1,595	714	1,595	714
Unallocated Financing Receivables [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	0	1,707	0	1,707	$ 149	9	$ 612	$ 581	$ 1,150
Financing Receivable, Allowance for Credit Loss, Writeoff	0	0	0	0
Financing Receivable, Allowance for Credit Loss, Recovery	0	0	0	0
Provision for credit losses	(149)	1,126	(9)	557
Allowance on Individually Measured Loans	0	0	0	0
Allowance on Collectively Measured Loans	$ 0	$ 1,707	$ 0	$ 1,707
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)