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, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 9,688,947			$ 8,743,465
Financing Receivable, Allowance for Credit Loss	(156,968)	$ (151,546)	$ (85,600)	(83,968)	$ (82,660)	$ (80,517)	$ (83,369)
Loans and Leases Receivable, Net Amount	9,531,979			8,659,497
Loans held for sale	24,407			17,718
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	4,027,035			3,945,853
Financing Receivable, Allowance for Credit Loss	(61,324)	(50,233)	(27,873)	(20,340)	(17,922)	(15,648)	(14,766)
Commercial Business [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	3,836,009			2,989,613
Financing Receivable, Allowance for Credit Loss	(50,572)	(53,186)	(31,054)	(30,292)	(30,879)	(29,700)	(34,658)
Agriculture [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	850,290			765,371
Financing Receivable, Allowance for Credit Loss	(12,461)	(14,868)	(6,510)	(15,835)	(13,899)	(12,671)	(9,589)
Construction [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	273,176			361,533
Financing Receivable, Allowance for Credit Loss	(8,963)	(7,953)	(6,821)	(8,571)	(11,852)	(12,457)	(14,395)
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	665,432			637,325
Financing Receivable, Allowance for Credit Loss	(22,107)	(23,711)	(11,672)	(7,435)	(7,458)	(7,619)	(8,024)
Consumer Loan [Member]
Financing Receivable, Credit Quality Indicator - interest written off on nonaccrual loans [Line Items]
Loans and Leases Receivable, Net of Deferred Income	37,005			43,770
Financing Receivable, Allowance for Credit Loss	$ (1,541)	$ (1,595)	$ (1,661)	$ (883)	$ (579)	$ (715)	$ (787)