Fair Values of Financial Instruments - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Investment securities available for sale	$ 1,142,195	$ 999,947
Investment securities held to maturity	489,217	568,208
Loans held for sale	4,778	7,216
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	139,247	154,905
Interest-bearing time deposits	36,963	35,027
Investment securities available for sale
Liabilities:
Deposits	6,267,879	5,741,019
Significant Other Observable Inputs (Level 2)
Assets:
Investment securities available for sale	1,138,867	995,969
Investment securities held to maturity	481,377	556,305
Loans held for sale	4,778	7,216
Federal Home Loan Bank stock	24,588	23,825
Interest rate swap asset	12,083	7,323
Interest receivable	40,881	37,130
Liabilities:
Deposits	1,464,129	1,406,526
Borrowings:
Federal funds purchased	104,000	144,038
Securities sold under repurchase agreements	113,437	136,562
Federal Home Loan Bank advances	318,728	361,085
Subordinated debentures and term loans	127,298	120,085
Interest rate swap liability	12,636	8,688
Interest payable	5,607	4,390
Significant Unobservable Inputs (Level 3)
Assets:
Investment securities available for sale	3,328	3,978
Investment securities held to maturity	7,840	11,903
Loans	7,004,193	6,534,877
Carrying Amount
Assets:
Cash and cash equivalents	139,247	154,905
Interest-bearing time deposits	36,963	35,027
Investment securities available for sale	1,142,195	999,947
Investment securities held to maturity	490,387	560,655
Loans held for sale	4,778	7,216
Loans	7,143,915	6,676,167
Federal Home Loan Bank stock	24,588	23,825
Interest rate swap asset	12,083	7,323
Interest receivable	40,881	37,130
Liabilities:
Deposits	7,754,593	7,172,530
Borrowings:
Federal funds purchased	104,000	144,038
Securities sold under repurchase agreements	113,512	136,623
Federal Home Loan Bank advances	314,986	414,377
Subordinated debentures and term loans	138,463	139,349
Interest rate swap liability	12,636	8,688
Interest payable	$ 5,607	$ 4,390

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Interest Bearing Deposits with Banks, Fair Value Disclosure

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Interest Payable Fair Value Disclosure

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

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

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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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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The face amount of loans that will be sold to other entities.

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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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