Disclosures About Fair Value of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets:
Investment securities available for sale	$ 1,646,399	$ 1,142,195
Investment securities held to maturity	865,286	489,217
Loans held for sale	7,910	4,778
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	202,383	139,247
Interest-bearing time deposits	230,101	36,963
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 rate swap and cap asset	0	0
Interest receivable	0	0
Liabilities:
Deposits	7,992,716	6,267,879
Borrowings:
Federal funds purchased	0	0
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 time deposits	0	0
Investment securities available for sale	1,643,503	1,138,867
Investment securities held to maturity	832,750	481,377
Loans held for sale	7,910	4,778
Loans	0	0
Federal Home Loan Bank stock	28,736	24,588
Interest rate swap and cap asset	37,899	12,083
Interest receivable	45,923	40,881
Liabilities:
Deposits	1,752,081	1,464,129
Borrowings:
Federal funds purchased	0	104,000
Securities sold under repurchase agreements	191,603	113,437
Federal Home Loan Bank advances	357,166	318,728
Subordinated debentures and term loans	124,453	127,298
Interest rate swap liability	39,629	12,636
Interest payable	7,855	5,607
Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Interest-bearing time deposits	0	0
Investment securities available for sale	2,896	3,328
Investment securities held to maturity	32,536	7,840
Loans held for sale	0	0
Loans	8,206,069	7,004,193
Federal Home Loan Bank stock	0	0
Interest rate swap and cap asset	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 term loans	0	0
Interest rate swap liability	0	0
Interest payable	0	0
Carrying Amount
Assets:
Cash and cash equivalents	202,383	139,247
Interest-bearing time deposits	230,101	36,963
Investment securities available for sale	1,646,399	1,142,195
Investment securities held to maturity	843,021	490,387
Loans held for sale	7,910	4,778
Loans	8,218,689	7,143,915
Federal Home Loan Bank stock	28,736	24,588
Interest rate swap and cap asset	37,899	12,083
Interest receivable	45,923	40,881
Liabilities:
Deposits	9,765,451	7,754,593
Borrowings:
Federal funds purchased	0	104,000
Securities sold under repurchase agreements	191,603	113,512
Federal Home Loan Bank advances	354,609	314,986
Subordinated debentures and term loans	138,630	138,463
Interest rate swap liability	39,629	12,636
Interest payable	$ 7,855	$ 5,607

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

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