Loans (Analysis of the Aged Loan Portfolio) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current Loans	$ 9,625,411	$ 8,686,523
Past Due Loans	16,305	23,882
Nonaccrual Loans	47,231	33,060
Total Loans	9,688,947	8,743,465
Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	4,015,038	3,935,633
Past Due Loans	1,635	6,421
Nonaccrual Loans	10,362	3,799
Total Loans	4,027,035	3,945,853
Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	3,808,794	2,959,826
Past Due Loans	7,902	8,850
Nonaccrual Loans	19,313	20,937
Total Loans	3,836,009	2,989,613
Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	833,408	755,719
Past Due Loans	1,969	4,629
Nonaccrual Loans	14,913	5,023
Total Loans	850,290	765,371
Construction [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	272,959	360,582
Past Due Loans	0	951
Nonaccrual Loans	217	0
Total Loans	273,176	361,533
One-to-Four Family Residential [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	658,468	631,109
Past Due Loans	4,559	2,924
Nonaccrual Loans	2,405	3,292
Total Loans	665,432	637,325
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Current Loans	36,744	43,654
Past Due Loans	240	107
Nonaccrual Loans	21	9
Total Loans	37,005	43,770
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	14,018	18,332
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	547	6,421
Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	6,987	6,081
Financial Asset, 30 to 59 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,710	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	4,559	2,516
Financial Asset, 30 to 59 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	215	80
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	2,287	5,550
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	1,088	0
Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Business [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	915	2,769
Financial Asset, 60 to 89 Days Past Due [Member] | Agriculture [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	259	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	0	408
Financial Asset, 60 to 89 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due Loans	25	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