Loans Receivable and the Allowance for Credit Losses - Nonaccrual Status and Interest Income (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	$ 43,973	$ 41,483
Nonaccrual with no Allowance for Credit Losses	28,418
90 Days or More Past Due And Accruing	303	136
Interest Income Recognized on Nonaccrual	272
Agricultural
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	3,585	2,894
Nonaccrual with no Allowance for Credit Losses	2,519
90 Days or More Past Due And Accruing	0	0
Interest Income Recognized on Nonaccrual	64
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	11,755	13,276
Nonaccrual with no Allowance for Credit Losses	6,140
90 Days or More Past Due And Accruing	62	0
Interest Income Recognized on Nonaccrual	56
Commercial real estate
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	25,066	22,037
Nonaccrual with no Allowance for Credit Losses	19,152
90 Days or More Past Due And Accruing	174	0
Interest Income Recognized on Nonaccrual	141
Commercial real estate \| Construction & development
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	867	1,494
Nonaccrual with no Allowance for Credit Losses	701
90 Days or More Past Due And Accruing	0	0
Interest Income Recognized on Nonaccrual	35
Commercial real estate \| Farmland
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	13,682	10,402
Nonaccrual with no Allowance for Credit Losses	11,566
90 Days or More Past Due And Accruing	0	0
Interest Income Recognized on Nonaccrual	84
Commercial real estate \| Multifamily
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	0	0
Nonaccrual with no Allowance for Credit Losses	0
90 Days or More Past Due And Accruing	0	0
Interest Income Recognized on Nonaccrual	1
Commercial real estate \| Commercial real estate-other
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	10,517	10,141
Nonaccrual with no Allowance for Credit Losses	6,885
90 Days or More Past Due And Accruing	174	0
Interest Income Recognized on Nonaccrual	21
Residential real estate
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	3,345	3,070
Nonaccrual with no Allowance for Credit Losses	582
90 Days or More Past Due And Accruing	44	124
Interest Income Recognized on Nonaccrual	9
Residential real estate \| One- to four- family first liens
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	2,777	2,557
Nonaccrual with no Allowance for Credit Losses	581
90 Days or More Past Due And Accruing	44	99
Interest Income Recognized on Nonaccrual	8
Residential real estate \| One- to four- family junior liens
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	568	513
Nonaccrual with no Allowance for Credit Losses	1
90 Days or More Past Due And Accruing	0	25
Interest Income Recognized on Nonaccrual	1
Consumer
Financing Receivable, Recorded Investment, Past Due
Nonaccrual	222	206
Nonaccrual with no Allowance for Credit Losses	25
90 Days or More Past Due And Accruing	23	$ 12
Interest Income Recognized on Nonaccrual	$ 2

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