Fair Values of Financial Instruments - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Investment securities available for sale	$ 2,344,551	$ 1,919,119
Investment securities held to maturity	2,202,503	1,280,293
Loans held for sale	11,187	3,966
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	167,146	192,896
Interest-bearing deposits	474,154	392,305
Investment securities available for sale	999	0
Investment securities held to maturity	0	0
Loans held for sale	0	0
Loans	0	0
Federal Home Loan Bank stock	0	0
Asset Derivatives	0	0
Interest receivable	0	0
Liabilities at December 31:
Deposits	12,038,992	10,482,865
Borrowings:
Securities sold under repurchase agreements	0	0
Federal Home Loan Bank advances	0	0
Subordinated debentures and term loans	0	0
Interest rate swap liability	0	0
Interest payable	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	0	0
Interest-bearing deposits	0	0
Investment securities available for sale	2,338,061	1,916,640
Investment securities held to maturity	2,188,600	1,260,815
Loans held for sale	11,187	3,966
Loans	0	0
Federal Home Loan Bank stock	28,736	28,736
Asset Derivatives	41,133	74,335
Interest receivable	57,187	53,948
Liabilities at December 31:
Deposits	690,089	878,257
Borrowings:
Securities sold under repurchase agreements	181,572	177,097
Federal Home Loan Bank advances	337,005	399,991
Subordinated debentures and term loans	107,892	108,439
Interest rate swap liability	41,968	76,353
Interest payable	2,762	3,287
Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Interest-bearing deposits	0	0
Investment securities available for sale	5,491	2,479
Investment securities held to maturity	13,903	19,478
Loans held for sale	0	0
Loans	9,068,319	9,191,628
Federal Home Loan Bank stock	0	0
Asset Derivatives	0	0
Interest receivable	0	0
Liabilities at December 31:
Deposits	0	0
Borrowings:
Securities sold under repurchase agreements	0	0
Federal Home Loan Bank advances	0	0
Subordinated debentures and term loans	0	0
Interest rate swap liability	0	0
Interest payable	0	0
Carrying Amount
Assets:
Cash and cash equivalents	167,146	192,896
Interest-bearing deposits	474,154	392,305
Investment securities available for sale	2,344,551	1,919,119
Investment securities held to maturity	2,179,802	1,227,668
Loans held for sale	11,187	3,966
Loans	9,046,464	9,112,526
Federal Home Loan Bank stock	28,736	28,736
Asset Derivatives	41,133	74,335
Interest receivable	57,187	53,948
Liabilities at December 31:
Deposits	12,732,577	11,361,610
Borrowings:
Securities sold under repurchase agreements	181,577	177,102
Federal Home Loan Bank advances	334,055	389,430
Subordinated debentures and term loans	118,618	118,380
Interest rate swap liability	41,968	76,353
Interest payable	$ 2,762	$ 3,287

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