Fair Value - Estimated fair value and related carrying amount, of the Company's financial instruments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Financial assets:
Loans held for sale	$ 87,393	$ 33,752	$ 22,925
Financial liabilities:
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	269,072	279,698	270,649
Increase (Decrease) in Loans Held-for-sale	280,684	283,331
Other borrowings	815,771	115,919	266,084
Carrying Amount
Financial assets:
Cash and cash equivalents	719,194	307,309	408,983
Investment securities	1,862,258	1,571,010	1,542,671
Loans held for sale	87,393	33,752	22,925
Loans, net of allowance for loan losses (1)	11,229,892	10,855,344	10,962,037
Accrued interest receivable	36,131	34,808	35,997
Mortgage servicing rights	28,674	36,056	34,727
Interest rate swap - non-designated hedge	21,700	9,268	3,824
Other derivative financial instruments (mortgage banking related)	2,702	747	1,267
Financial liabilities:
Deposits	12,023,787	11,613,875	11,646,933
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	269,072	279,698	270,649
Other borrowings	815,771	115,919	266,084
Accrued interest payable	5,036	4,279	4,719
Interest rate swap - non-designated hedge	23,723	9,460	4,373
Interest rate swap - cash flow hedge	19,564	82	48
Other derivative financial instruments (Mortgage banking related)	86	493
Fair Value
Financial assets:
Cash and cash equivalents	719,194	307,309	408,983
Investment securities	1,862,258	1,571,010	1,542,671
Loans held for sale	87,393	33,752	22,925
Loans, net of allowance for loan losses (1)	11,259,351	10,640,774	10,613,571
Accrued interest receivable	36,131	34,808	35,997
Mortgage servicing rights	28,674	36,056	34,727
Interest rate swap - non-designated hedge	21,700	9,268	3,824
Other derivative financial instruments (mortgage banking related)	2,702	747	1,267
Financial liabilities:
Deposits	11,302,479	10,617,021	10,561,394
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	269,072	279,698	270,649
Other borrowings	818,294	119,017	269,134
Accrued interest payable	5,036	4,279	4,719
Interest rate swap - non-designated hedge	23,723	9,460	4,373
Interest rate swap - cash flow hedge	19,564	82	48
Other derivative financial instruments (Mortgage banking related)	86	493
Commitments to extend credit | Fair Value
Financial liabilities:
Commitments to extend credit	7,622	(56,732)	(88,424)
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	719,194	307,309	408,983
Investment securities	49,124	19,229	25,604
Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities	1,813,134	1,551,781	1,517,067
Loans held for sale	87,393	33,752	22,925
Accrued interest receivable	7,528	6,419	6,908
Interest rate swap - non-designated hedge	21,700	9,268	3,824
Other derivative financial instruments (mortgage banking related)	2,702	747	1,267
Financial liabilities:
Deposits	11,302,479	10,617,021	10,561,394
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	269,072	279,698	270,649
Other borrowings	818,294	119,017	269,134
Accrued interest payable	5,036	4,279	4,719
Interest rate swap - non-designated hedge	23,723	9,460	4,373
Interest rate swap - cash flow hedge	19,564	82	48
Other derivative financial instruments (Mortgage banking related)	86	493
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	7,622	(56,732)	(88,424)
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses (1)	11,259,351	10,640,774	10,613,571
Accrued interest receivable	28,603	28,389	29,089
Mortgage servicing rights	$ 28,674	$ 36,056	$ 34,727