FAIR VALUE, Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Carrying Value [Member]
Financial assets [Abstract]
Net loans	$ 6,810,440	$ 6,840,632
Financial liabilities [Abstract]
Deposits	9,303,982	8,994,967
Overnight Federal Home Loan Bank borrowings	0	8,300
Securities sold under agreement to repurchase, short-term	204,991	241,708
Other Federal Home Loan Bank borrowings	3,727	3,750
Subordinated notes payable	13,775	13,795
Subordinated debt held by unconsolidated subsidiary trusts	77,320	77,320
Fair Value [Member]
Financial assets [Abstract]
Net loans	7,063,785	7,028,663
Financial liabilities [Abstract]
Deposits	9,319,783	8,997,551
Overnight Federal Home Loan Bank borrowings	0	8,300
Securities sold under agreement to repurchase, short-term	204,991	241,708
Other Federal Home Loan Bank borrowings	3,789	3,755
Subordinated notes payable	13,775	13,795
Subordinated debt held by unconsolidated subsidiary trusts	$ 77,320	$ 77,320