FAIR VALUE, Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying Value [Member]
Financial assets [Abstract]
Net loans	$ 6,209,174	$ 4,901,329
Financial liabilities [Abstract]
Deposits	8,444,420	7,075,954
Short-term borrowings	24,000	146,200
Securities sold under agreement to repurchase, short-term	337,011	0
Other long-term debt	2,071	0
Subordinated debt held by unconsolidated subsidiary trusts	122,814	102,170
Fair Value [Member]
Financial assets [Abstract]
Net loans	6,244,941	4,935,140
Financial liabilities [Abstract]
Deposits	8,431,481	7,071,191
Short-term borrowings	24,000	146,200
Securities sold under agreement to repurchase, short-term	337,011	0
Other long-term debt	2,021	0
Subordinated debt held by unconsolidated subsidiary trusts	$ 122,814	$ 90,144