FAIR VALUE, Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Carrying Value [Member]
Financial assets [Abstract]
Net loans	$ 6,260,737	$ 4,901,329
Financial liabilities [Abstract]
Deposits	8,605,990	7,075,954
Short-term borrowings	0	146,200
Securities sold under agreement to repurchase, short-term	310,703	0
Other long-term debt	3,586	0
Subordinated debt held by unconsolidated subsidiary trusts	122,808	102,170
Fair Value [Member]
Financial assets [Abstract]
Net loans	6,321,781	4,935,140
Financial liabilities [Abstract]
Deposits	8,592,459	7,071,191
Short-term borrowings	0	146,200
Securities sold under agreement to repurchase, short-term	310,703	0
Other long-term debt	3,568	0
Subordinated debt held by unconsolidated subsidiary trusts	$ 122,808	$ 90,144