Fair Value - Estimated fair value and related carrying amount, of the Company’s financial instruments - (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jan. 03, 2017	Dec. 31, 2016
Financial assets:
Loans held for sale	$ 46,321	$ 57,052		$ 50,572
Financial liabilities:
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	291,099	305,268	$ 1,014	313,773
Increase (Decrease) in Loans Held-for-sale	533,647	533,393
Other borrowings	83,307	55,306		55,358
Carrying Amount
Financial assets:
Cash and cash equivalents	403,934	507,517		374,448
Investment securities	1,336,796	941,707		1,014,981
Loans held for sale	46,321	57,052		50,572
Loans, net of allowance for loan losses	8,223,204	6,489,068		6,643,326
Interest Receivable	25,172	17,501		18,618
Mortgage servicing rights	29,937	23,064		29,037
Interest rate swap - non-designated hedge	200			203
Other derivative financial instruments (Mortgage - banking related)	1,292	3,091		2,403
Financial liabilities:
Deposits	9,062,021	7,247,406		7,334,423
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	291,099	305,268		313,773
Other borrowings	83,307	55,306		55,358
Interest Payable	1,810	1,384		1,359
Interest rate swap - non-designated hedge	197			181
Interest rate swap - cash flow hedge	329	655		498
Other derivative financial instruments (Mortgage banking related)	775	444		51
Fair Value.
Financial assets:
Cash and cash equivalents	403,934	507,517		374,448
Investment securities	1,336,850	941,932		1,015,137
Loans held for sale	46,321	57,052		50,572
Loans, net of allowance for loan losses	8,284,002	6,667,622		6,649,575
Interest Receivable	25,172	17,501		18,618
Mortgage servicing rights	29,937	23,064		29,037
Interest rate swap - non-designated hedge	200			203
Other derivative financial instruments (Mortgage - banking related)	1,292	3,091		2,403
Financial liabilities:
Deposits	8,512,681	7,015,012		6,935,867
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	291,099	305,268		313,773
Other borrowings	85,344	49,781		54,379
Interest Payable	1,810	1,384		1,359
Interest rate swap - non-designated hedge	197			181
Interest rate swap - cash flow hedge	329	655		498
Other derivative financial instruments (Mortgage banking related)	775	444		51
Commitments to extend credit | Fair Value.
Financial liabilities:
Commitments to extend credit	15,968			1,587
Standby letters of credit and financial guarantees | Fair Value.
Financial liabilities:
Commitments to extend credit		45,285
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	403,934	507,517		374,448
Investment securities	14,171	12,050		12,041
Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities	1,322,679	929,882		1,003,096
Loans held for sale	46,321	57,052		50,572
Interest Receivable	5,373	3,528		3,642
Interest rate swap - non-designated hedge	200			203
Other derivative financial instruments (Mortgage - banking related)	1,292	3,091		2,403
Financial liabilities:
Deposits	8,512,681	7,015,012		6,935,867
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	291,099	305,268		313,773
Other borrowings	85,344	49,781		54,379
Interest Payable	1,810	1,384		1,359
Interest rate swap - non-designated hedge	197			181
Interest rate swap - cash flow hedge	329	655		498
Other derivative financial instruments (Mortgage banking related)	775	444		51
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	15,968			1,587
Significant Other Observable Inputs (Level 2) | Standby letters of credit and financial guarantees
Financial liabilities:
Commitments to extend credit		45,285
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses	8,284,002	6,667,622		6,649,575
Interest Receivable	19,799	13,973		14,976
Mortgage servicing rights	29,937	23,064		29,037
Recurring basis
Financial assets:
Loans held for sale	46,321	57,052		50,572
Mortgage servicing rights	29,937	23,064		29,037
Recurring basis | Significant Other Observable Inputs (Level 2)
Financial assets:
Loans held for sale	46,321	57,052		50,572
Recurring basis | Significant Unobservable Inputs (Level 3)
Financial assets:
Mortgage servicing rights	$ 29,937	$ 23,064		$ 29,037