Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Loans (Analysis of Loan Portfolio by Major Types of Loans) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 9,521,385		$ 9,427,660
Financing Receivable, Allowance for Credit Loss	(142,785)	$ (142,988)	(149,140)	$ (156,968)	$ (151,546)	$ (83,968)
Loans and Leases Receivable, Net Amount	9,378,600		9,278,520
Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	4,088,484		4,062,313
Financing Receivable, Allowance for Credit Loss	(51,752)	(53,250)	(68,934)	(61,324)	(50,233)	(20,340)
Commercial Business [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,436,351		3,597,968
Financing Receivable, Allowance for Credit Loss	(55,561)	(57,554)	(45,250)	(50,572)	(53,186)	(30,292)
Agriculture [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	815,985		779,627
Financing Receivable, Allowance for Credit Loss	(8,965)	(7,920)	(9,052)	(12,461)	(14,868)	(15,835)
Construction [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	326,569		268,663
Financing Receivable, Allowance for Credit Loss	(6,367)	(6,559)	(7,636)	(8,963)	(7,953)	(8,571)
One-to-Four Family Residential [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	823,877		683,570
Financing Receivable, Allowance for Credit Loss	(18,855)	(16,519)	(16,875)	(22,107)	(23,711)	(7,435)
Consumer Loan [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	30,119		35,519
Financing Receivable, Allowance for Credit Loss	$ (1,285)	$ (1,186)	$ (1,393)	$ (1,541)	$ (1,595)	$ (883)