Loans and Allowance for Loan Losses - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Interest receivable	$ 36,596,000		$ 36,596,000			$ 38,708,000
Reversal of interest income on nonaccrual loans	12,000	$ 14,000	25,000	$ 143,000
Nonaccrual loans, no allowance	1,400,000		1,400,000			2,200,000
Collateral-dependent loans	10,100,000		10,100,000			11,500,000
Commitments to lend additional funds on Troubled Debt Restructurings (TDR)	0	0	0	0
Mortgage Loans in Process of Foreclosure, Amount	34,000		34,000			1,200,000
Accrued interest receivable on our loan portfolio	13,400,000		13,400,000			16,400,000
TDRs in default	230,000		230,000
Allowance for Credit Loss	42,913,000	59,868,000	42,913,000	59,868,000	$ 41,454,000	49,006,000	$ 53,638,000	$ 24,797,000
COVID-19 Payment Deferral
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	182,000		182,000			47,200,000
Commercial Real Estate Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Owner and nonowner-occupied real estate	1,240,000,000		1,240,000,000
Loans secured by multi-family properties	170,400,000		170,400,000
Loans secured by farmland	18,500,000		$ 18,500,000
General Loan Term			20 years
Allowance for Credit Loss	28,930,000	43,785,000	$ 28,930,000	43,785,000	27,236,000	35,709,000	36,120,000	9,572,000
1-4 Family Residential Real Estate Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	2,520,000	2,702,000	$ 2,520,000	2,702,000	2,508,000	2,270,000	2,640,000	3,833,000
1-4 Family Residential Real Estate Loans | Minimum
Financing Receivable, Allowance for Credit Loss [Line Items]
General Loan Term			5 years
1-4 Family Residential Real Estate Loans | Maximum
Financing Receivable, Allowance for Credit Loss [Line Items]
General Loan Term			30 years
Paycheck Protection Program
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	132,100,000		$ 132,100,000			214,800,000
Allowance for Credit Loss	0		0
Commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	$ 3,097,000	$ 4,221,000	$ 3,097,000	$ 4,221,000	$ 3,108,000	$ 4,107,000	$ 4,519,000	$ 6,351,000