Loans and Allowance for Loan Losses - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Interest receivable	$ 29,097,000		$ 29,097,000			$ 38,708,000
Reversal of interest income on nonaccrual loans	5,000	$ 0	13,000	$ 147,000
Nonaccrual loans, no allowance	1,100,000		1,100,000			2,200,000
Collateral-dependent loans	9,100,000		9,100,000			11,500,000
Commitments to lend additional funds on Troubled Debt Restructurings (TDR)	0	0	0	0
Mortgage Loans in Process of Foreclosure, Amount	0		0			1,200,000
Accrued interest receivable on our loan portfolio	13,300,000		13,300,000			16,400,000
Allowance for Credit Loss	38,022,000	55,110,000	38,022,000	55,110,000	$ 42,913,000	49,006,000	$ 59,868,000	$ 24,797,000
COVID-19 Payment Deferral
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0		0			47,200,000
Commercial Real Estate Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Owner and nonowner-occupied real estate	1,320,000,000		1,320,000,000
Loans secured by multi-family properties	260,100,000		260,100,000
Loans secured by farmland	22,000,000		$ 22,000,000
General Loan Term			20 years
Allowance for Credit Loss	28,258,000	41,785,000	$ 28,258,000	41,785,000	28,930,000	35,709,000	43,785,000	9,572,000
1-4 Family Residential Real Estate Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	1,946,000	2,635,000	$ 1,946,000	2,635,000	2,520,000	2,270,000	2,702,000	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	67,500,000		$ 67,500,000			214,800,000
Allowance for Credit Loss	0		0
Commercial loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	$ 2,560,000	$ 4,492,000	$ 2,560,000	$ 4,492,000	$ 3,097,000	$ 4,107,000	$ 4,221,000	$ 6,351,000