Disclosures About Fair Value of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets:
Investment securities available for sale	$ 2,426,900	$ 1,919,119
Investment securities held to maturity	1,760,847	1,280,293
Loans held for sale	18,582	3,966
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	167,596	192,896
Interest-bearing deposits	438,863	392,305
Investment securities available for sale	0	0
Investment securities held to maturity	0	0
Loans held for sale	0	0
Loans, net	0	0
Federal Home Loan Bank stock	0	0
Interest rate swap asset	0	0
Interest receivable	0	0
Liabilities:
Deposits	11,419,155	10,482,865
Borrowings:
Securities sold under repurchase agreements	0	0
Federal Home Loan Bank advances	0	0
Subordinated debentures and other borrowings	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	2,421,105	1,916,640
Investment securities held to maturity	1,745,282	1,260,815
Loans held for sale	18,582	3,966
Loans, net	0	0
Federal Home Loan Bank stock	28,736	28,736
Interest rate swap asset	51,845	74,335
Interest receivable	54,173	53,948
Liabilities:
Deposits	782,802	878,257
Borrowings:
Securities sold under repurchase agreements	146,900	177,097
Federal Home Loan Bank advances	340,783	399,991
Subordinated debentures and other borrowings	107,751	108,439
Interest rate swap liability	53,309	76,353
Interest payable	2,929	3,287
Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Interest-bearing deposits	0	0
Investment securities available for sale	5,795	2,479
Investment securities held to maturity	15,565	19,478
Loans held for sale	0	0
Loans, net	8,976,919	9,191,628
Federal Home Loan Bank stock	0	0
Interest rate swap asset	0	0
Interest receivable	0	0
Liabilities:
Deposits	0	0
Borrowings:
Securities sold under repurchase agreements	0	0
Federal Home Loan Bank advances	0	0
Subordinated debentures and other borrowings	0	0
Interest rate swap liability	0	0
Interest payable	0	0
Carrying Amount
Assets:
Cash and cash equivalents	167,596	192,896
Interest-bearing deposits	438,863	392,305
Investment securities available for sale	2,426,900	1,919,119
Investment securities held to maturity	1,721,414	1,227,668
Loans held for sale	18,582	3,966
Loans, net	8,921,475	9,112,526
Federal Home Loan Bank stock	28,736	28,736
Interest rate swap asset	51,845	74,335
Interest receivable	54,173	53,948
Liabilities:
Deposits	12,203,400	11,361,610
Borrowings:
Securities sold under repurchase agreements	146,904	177,102
Federal Home Loan Bank advances	334,243	389,430
Subordinated debentures and other borrowings	118,498	118,380
Interest rate swap liability	53,309	76,353
Interest payable	$ 2,929	$ 3,287

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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