Fair Value - Estimated fair value and related carrying amount, of the Company’s financial instruments - (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financial assets:
Loans held for sale	$ 33,752	$ 46,321	$ 70,890
Financial liabilities:
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	279,698	291,099	286,857
Increase (Decrease) in Loans Held-for-sale	283,331	533,647
Other borrowings	115,919	83,307	216,385
Carrying Amount
Financial assets:
Cash and cash equivalents	307,309	403,934	377,627
Investment securities	1,571,010	1,336,796	1,673,769
Loans held for sale	33,752	46,321	70,890
Loans, net of allowance for loan losses	10,855,344	8,223,204	10,575,417
Interest Receivable	34,808	25,172	32,727
Mortgage servicing rights	36,056	29,937	31,119
Interest rate swap - non-designated hedge	9,268	200	2,367
Other derivative financial instruments (Mortgage - banking related)	747	1,292	939
Financial liabilities:
Deposits	11,613,875	9,062,021	11,532,766
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	279,698	291,099	286,857
Other borrowings	115,919	83,307	216,385
Interest Payable	4,279	1,810	2,789
Interest rate swap - non-designated hedge	9,460	197	2,750
Interest rate swap - cash flow hedge	82	329	246
Other derivative financial instruments (Mortgage banking related)	493	775	252
Fair Value
Financial assets:
Cash and cash equivalents	307,309	403,934	377,627
Investment securities	1,571,010	1,336,850	1,673,796
Loans held for sale	33,752	46,321	70,890
Loans, net of allowance for loan losses	10,640,774	8,284,002	10,724,264
Interest Receivable	34,808	25,172	32,727
Mortgage servicing rights	36,056	29,937	31,119
Interest rate swap - non-designated hedge	9,268	200	2,367
Other derivative financial instruments (Mortgage - banking related)	747	1,292	939
Financial liabilities:
Deposits	10,617,021	8,512,681	10,796,380
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	279,698	291,099	286,857
Other borrowings	119,017	85,344	219,421
Interest Payable	4,279	1,810	2,789
Interest rate swap - non-designated hedge	9,460	197	2,750
Interest rate swap - cash flow hedge	82	329	246
Other derivative financial instruments (Mortgage banking related)	493	775	252
Commitments to extend credit | Fair Value
Financial liabilities:
Commitments to extend credit	(56,732)	15,968	41,319
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	307,309	403,934	377,627
Investment securities	19,229	13,664	23,047
Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities	1,551,781	1,323,186	1,650,749
Loans held for sale	33,752	46,321	70,890
Interest Receivable	6,419	5,373	7,051
Interest rate swap - non-designated hedge	9,268	200	2,367
Other derivative financial instruments (Mortgage - banking related)	747	1,292	939
Financial liabilities:
Deposits	10,617,021	8,512,681	10,796,380
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	279,698	291,099	286,857
Other borrowings	119,017	85,344	219,421
Interest Payable	4,279	1,810	2,789
Interest rate swap - non-designated hedge	9,460	197	2,750
Interest rate swap - cash flow hedge	82	329	246
Other derivative financial instruments (Mortgage banking related)	493	775	252
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	(56,732)	15,968	41,319
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses	10,640,774	8,284,002	10,724,264
Interest Receivable	28,389	19,799	25,676
Mortgage servicing rights	$ 36,056	$ 29,937	$ 31,119