Loans (Analysis of the Aged Loan Portfolio) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current Loans	$ 9,693,807	$ 8,686,523
Past Due Loans	24,359	23,882
Nonaccrual Loans	53,732	33,060
Total Loans	9,771,898	8,743,465
Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	4,011,604	3,935,633
Past Due Loans	9,884	6,421
Nonaccrual Loans	11,155	3,799
Total Loans	4,032,643	3,945,853
Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	3,833,606	2,959,826
Past Due Loans	5,382	8,850
Nonaccrual Loans	20,525	20,937
Total Loans	3,859,513	2,989,613
Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	823,226	755,719
Past Due Loans	3,562	4,629
Nonaccrual Loans	19,162	5,023
Total Loans	845,950	765,371
Construction [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	303,798	360,582
Past Due Loans	0	951
Nonaccrual Loans	217	0
Total Loans	304,015	361,533
One-to-Four Family Residential [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	684,729	631,109
Past Due Loans	5,446	2,924
Nonaccrual Loans	2,662	3,292
Total Loans	692,837	637,325
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	36,844	43,654
Past Due Loans	85	107
Nonaccrual Loans	11	9
Total Loans	36,940	43,770
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	18,433	18,332
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	7,402	6,421
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	4,756	6,081
Financial Asset, 30 to 59 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,197	2,283
Financial Asset, 30 to 59 Days Past Due [Member] | Construction [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	951
Financial Asset, 30 to 59 Days Past Due [Member] | One-to-Four Family Residential [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	5,015	2,516
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	63	80
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	5,926	5,550
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,482	0
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	626	2,769
Financial Asset, 60 to 89 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,365	2,346
Financial Asset, 60 to 89 Days Past Due [Member] | Construction [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, 60 to 89 Days Past Due [Member] | One-to-Four Family Residential [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	431	408
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	22	27
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | One-to-Four Family Residential [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	0	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	$ 0	$ 0