Fair Value - Estimated fair value and related carrying amount, of the Company’s financial instruments - (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Financial assets:
Loans held for sale	$ 36,968	$ 65,995	$ 70,890
Financial liabilities:
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	331,969	334,018	286,857
Increase (Decrease) in Loans Held-for-sale	207,909	449,052
Other borrowings	115,754	98,147	216,385
Carrying Amount
Financial assets:
Cash and cash equivalents	396,849	431,890	377,627
Investment securities	1,597,727	1,358,894	1,673,769
Loans held for sale	36,968	65,995	70,890
Loans, net of allowance for loan losses	10,778,068	8,140,706	10,575,417
Interest Receivable	33,751	23,469	32,727
Mortgage servicing rights	35,107	29,930	31,119
Interest rate swap - non-designated hedge	7,750	208	2,367
Other derivative financial instruments (Mortgage - banking related)	1,098	1,748	939
Financial liabilities:
Deposits	11,638,289	9,031,654	11,532,766
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	331,969	334,018	286,857
Other borrowings	115,754	98,147	216,385
Interest Payable	3,882	1,502	2,789
Interest rate swap - non-designated hedge	7,981	203	2,750
Interest rate swap - cash flow hedge	116	389	246
Other derivative financial instruments (Mortgage banking related)			252
Fair Value.
Financial assets:
Cash and cash equivalents	396,849	431,890	377,627
Investment securities	1,597,731	1,358,976	1,673,796
Loans held for sale	36,968	65,995	70,890
Loans, net of allowance for loan losses	10,547,778	8,216,793	10,724,264
Interest Receivable	33,751	23,469	32,727
Mortgage servicing rights	35,107	29,930	31,119
Interest rate swap - non-designated hedge	7,750	208	2,367
Other derivative financial instruments (Mortgage - banking related)	1,098	1,748	939
Financial liabilities:
Deposits	10,675,705	8,481,700	10,796,380
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	331,969	334,018	286,857
Other borrowings	119,221	100,723	219,421
Interest Payable	3,882	1,502	2,789
Interest rate swap - non-designated hedge	7,981	203	2,750
Interest rate swap - cash flow hedge	116	389	246
Other derivative financial instruments (Mortgage banking related)			252
Commitments to extend credit | Fair Value.
Financial liabilities:
Commitments to extend credit	(62,060)	17,200	41,319
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	396,849	431,890	377,627
Investment securities	19,229	14,301	23,047
Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities	1,578,502	1,344,675	1,650,749
Loans held for sale	36,968	65,995	70,890
Interest Receivable	7,333	5,454	7,051
Interest rate swap - non-designated hedge	7,750	208	2,367
Other derivative financial instruments (Mortgage - banking related)	1,098	1,748	939
Financial liabilities:
Deposits	10,675,705	8,481,700	10,796,380
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	331,969	334,018	286,857
Other borrowings	119,221	100,723	219,421
Interest Payable	3,882	1,502	2,789
Interest rate swap - non-designated hedge	7,981	203	2,750
Interest rate swap - cash flow hedge	116	389	246
Other derivative financial instruments (Mortgage banking related)			252
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	(62,060)	17,200	41,319
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses	10,547,778	8,216,793	10,724,264
Interest Receivable	26,418	18,015	25,676
Mortgage servicing rights	$ 35,107	$ 29,930	$ 31,119