Fair Value - Estimated fair value and related carrying amount, of the Company's financial instruments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Financial assets:
Loans held for sale	$ 71,719	$ 33,297	$ 59,363
Interest Receivable	30,200
Financial liabilities:
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	325,723	276,891	298,741
Increase (Decrease) in Loans Held-for-sale	129,458	127,840
Other borrowings	1,316,100	616,250	815,936
Carrying Amount
Financial assets:
Cash and cash equivalents	1,262,836	949,591	688,704
Investment securities	2,034,189	1,506,873	2,005,171
Loans held for sale	71,719		59,363
Loans held for sale		33,297
Loans, net of allowance for loan losses	11,362,105	11,089,600	11,313,113
Accrued interest receivable	37,696	36,965	36,774
Mortgage servicing rights	26,365	32,415	30,525
Interest rate swap - non-designated hedge	51,244	6,672	15,350
Interest rate swap - cash flow hedge		217
Other derivative financial instruments (mortgage banking related)	9,909	1,838	902
Financial liabilities:
Deposits	12,344,547	11,918,971	12,177,096
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	325,723		298,741
Federal funds purchased and securities sold under agreements to repurchase		276,891
Other borrowings	1,316,100		815,936
Other borrowings		616,250
Accrued interest payable	4,063	5,688	4,916
Interest rate swap - non-designated hedge	54,836	7,403	16,693
Interest rate swap - cash flow hedge	43,025	2,927	13,791
Other derivative financial instruments (Mortgage banking related)			789
Fair Value
Financial assets:
Cash and cash equivalents	1,262,836	949,591	688,704
Investment securities	2,034,189	1,506,873	2,005,171
Loans held for sale	71,719		59,363
Loans held for sale		33,297
Loans, net of allowance for loan losses	11,338,975	11,005,731	11,452,003
Accrued interest receivable	37,696	36,965	36,774
Mortgage servicing rights	26,365	32,415	30,525
Interest rate swap - non-designated hedge	51,244	6,672	15,350
Interest rate swap - cash flow hedge		217
Other derivative financial instruments (mortgage banking related)	9,909	1,838	902
Financial liabilities:
Deposits	11,911,840	10,956,761	11,406,477
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	325,723		298,741
Federal funds purchased and securities sold under agreements to repurchase		276,891
Other borrowings	1,318,621		818,210
Other borrowings		619,140
Accrued interest payable	4,063	5,688	4,916
Interest rate swap - non-designated hedge	54,836	7,403	16,693
Interest rate swap - cash flow hedge	43,025	2,927	13,791
Other derivative financial instruments (Mortgage banking related)			789
Commitments to extend credit		(21,189)
Commitments to extend credit | Fair Value
Financial liabilities:
Commitments to extend credit	(6,109)		36,031
Quoted Prices In Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents	1,262,836	949,591	688,704
Investment securities	62,994	40,624	49,124
Accrued interest receivable		524
Significant Other Observable Inputs (Level 2)
Financial assets:
Investment securities	1,971,195	1,466,249	1,956,047
Loans held for sale	71,719		59,363
Loans held for sale		33,297
Accrued interest receivable	7,752	5,891	8,500
Interest rate swap - non-designated hedge	51,244	6,672	15,350
Interest rate swap - cash flow hedge		217
Other derivative financial instruments (mortgage banking related)	9,909	1,838	902
Financial liabilities:
Deposits	11,911,840	10,956,761	11,406,477
Federal Funds Purchased and Securities Sold under Agreements to Repurchase.	325,723		298,741
Federal funds purchased and securities sold under agreements to repurchase		276,891
Other borrowings	1,318,621		818,210
Other borrowings		619,140
Accrued interest payable	4,063	5,688	4,916
Interest rate swap - non-designated hedge	54,836	7,403	16,693
Interest rate swap - cash flow hedge	43,025	2,927	13,791
Other derivative financial instruments (Mortgage banking related)			789
Commitments to extend credit		(21,189)
Significant Other Observable Inputs (Level 2) | Commitments to extend credit
Financial liabilities:
Commitments to extend credit	(6,109)		36,031
Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net of allowance for loan losses	11,338,975	11,005,731	11,452,003
Accrued interest receivable	29,944	30,550	28,274
Mortgage servicing rights	$ 26,365	$ 32,415	$ 30,525