FAIR VALUE, Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Carrying Value [Member]
Financial assets [Abstract]
Net loans	$ 6,216,979	$ 6,231,837
Financial liabilities [Abstract]
Deposits	8,619,662	8,322,371
Short-term borrowings	0	54,400
Securities sold under agreement to repurchase, short-term	249,880	259,367
Other long-term debt	1,953	1,976
Subordinated debt held by unconsolidated subsidiary trusts	97,939	97,939
Fair Value [Member]
Financial assets [Abstract]
Net loans	6,266,587	6,247,939
Financial liabilities [Abstract]
Deposits	8,607,827	8,308,765
Short-term borrowings	0	54,400
Securities sold under agreement to repurchase, short-term	249,880	259,367
Other long-term debt	1,914	1,921
Subordinated debt held by unconsolidated subsidiary trusts	$ 97,939	$ 97,939