Disclosures About Fair Value of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Investment securities available for sale	$ 1,824,160	$ 1,790,025
Investment securities held to maturity	1,152,518	827,566
Loans held for sale	3,183	9,037
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	164,632	177,201
Interest-bearing deposits	273,936	118,263
Investment securities available for sale	0	0
Investment securities held to maturity	0	0
Loans held for sale	0	0
Loans	0	0
Federal Home Loan Bank stock	0	0
Interest receivable	0	0
Liabilities:
Deposits	9,797,840	8,146,745
Borrowings:
Federal funds purchased	0	0
Securities sold under repurchase agreements	0	0
Federal Home Loan Bank advances	0	0
Subordinated debentures and other borrowings	0	0
Interest payable	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Interest rate swap
Assets:
Interest rate swap asset	0	0
Borrowings:
Interest rate swap liability	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	1,821,673	1,787,132
Investment securities held to maturity	1,131,014	799,884
Loans held for sale	3,183	9,037
Loans	0	0
Federal Home Loan Bank stock	28,736	28,736
Interest receivable	52,992	48,901
Liabilities:
Deposits	1,108,656	1,675,202
Borrowings:
Federal funds purchased	80,000	55,000
Securities sold under repurchase agreements	187,732	187,801
Federal Home Loan Bank advances	413,532	352,581
Subordinated debentures and other borrowings	108,427	123,571
Interest payable	5,038	6,754
Significant Other Observable Inputs (Level 2) \| Interest rate swap
Assets:
Interest rate swap asset	82,010	27,855
Borrowings:
Interest rate swap liability	84,254	29,299
Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Interest-bearing deposits	0	0
Investment securities available for sale	2,487	2,893
Investment securities held to maturity	21,504	27,682
Loans held for sale	0	0
Loans	9,198,466	8,335,340
Federal Home Loan Bank stock	0	0
Interest receivable	0	0
Liabilities:
Deposits	0	0
Borrowings:
Federal funds purchased	0	0
Securities sold under repurchase agreements	0	0
Federal Home Loan Bank advances	0	0
Subordinated debentures and other borrowings	0	0
Interest payable	0	0
Significant Unobservable Inputs (Level 3) \| Interest rate swap
Assets:
Interest rate swap asset	0	0
Borrowings:
Interest rate swap liability	0	0
Carrying Amount
Assets:
Cash and cash equivalents	164,632	177,201
Interest-bearing deposits	273,936	118,263
Investment securities available for sale	1,824,160	1,790,025
Investment securities held to maturity	1,109,126	806,038
Loans held for sale	3,183	9,037
Loans	9,117,107	8,379,026
Federal Home Loan Bank stock	28,736	28,736
Interest receivable	52,992	48,901
Liabilities:
Deposits	10,906,153	9,839,956
Borrowings:
Federal funds purchased	80,000	55,000
Securities sold under repurchase agreements	187,732	187,946
Federal Home Loan Bank advances	399,522	351,072
Subordinated debentures and other borrowings	118,320	138,685
Interest payable	5,038	6,754
Carrying Amount \| Interest rate swap
Assets:
Interest rate swap asset	82,010	27,855
Borrowings:
Interest rate swap liability	$ 84,254	$ 29,299

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Interest Bearing Deposits with Banks, Fair Value Disclosure

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Amount 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 currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank.

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Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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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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Amount, before valuation allowance, of financing receivable classified as held-for-sale.

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Fair value portion of other liabilities.

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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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