Fair Values of Financial Instruments - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Investment securities available for sale	$ 1,790,025	$ 1,142,195
Investment securities held to maturity	827,566	489,217
Loans held for sale	9,037	4,778
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	177,201	139,247
Interest-bearing time deposits	118,263	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 asset	0	0
Interest receivable	0	0
Liabilities at December 31:
Deposits	8,146,745	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	1,787,132	1,138,867
Investment securities held to maturity	799,884	481,377
Loans held for sale	9,037	4,778
Loans	0	0
Federal Home Loan Bank stock	28,736	24,588
Interest rate swap asset	27,855	12,083
Interest receivable	48,901	40,881
Liabilities at December 31:
Deposits	1,675,202	1,464,129
Borrowings:
Federal funds purchased	55,000	104,000
Securities sold under repurchase agreements	187,801	113,437
Federal Home Loan Bank advances	352,581	318,728
Subordinated debentures and term loans	123,571	127,298
Interest rate swap liability	29,299	12,636
Interest payable	6,754	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	2,893	3,328
Investment securities held to maturity	27,682	7,840
Loans held for sale	0	0
Loans	8,335,340	7,004,193
Federal Home Loan Bank stock	0	0
Interest rate swap asset	0	0
Interest receivable	0	0
Liabilities at December 31:
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	177,201	139,247
Interest-bearing time deposits	118,263	36,963
Investment securities available for sale	1,790,025	1,142,195
Investment securities held to maturity	806,038	490,387
Loans held for sale	9,037	4,778
Loans	8,379,026	7,143,915
Federal Home Loan Bank stock	28,736	24,588
Interest rate swap asset	27,855	12,083
Interest receivable	48,901	40,881
Liabilities at December 31:
Deposits	9,839,956	7,754,593
Borrowings:
Federal funds purchased	55,000	104,000
Securities sold under repurchase agreements	187,946	113,512
Federal Home Loan Bank advances	351,072	314,986
Subordinated debentures and term loans	138,685	138,463
Interest rate swap liability	29,299	12,636
Interest payable	$ 6,754	$ 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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