FAIR VALUE, Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Value [Member]
Financial assets [Abstract]
Net loans	$ 6,178,927	$ 6,209,174
Financial liabilities [Abstract]
Deposits	8,771,092	8,444,420
Short-term borrowings	0	24,000
Securities sold under agreement to repurchase, short-term	279,702	337,011
Other long-term debt	2,042	2,071
Subordinated debt held by unconsolidated subsidiary trusts	122,820	122,814
Fair Value [Member]
Financial assets [Abstract]
Net loans	6,154,483	6,244,941
Financial liabilities [Abstract]
Deposits	8,754,350	8,431,481
Short-term borrowings	0	24,000
Securities sold under agreement to repurchase, short-term	279,702	337,011
Other long-term debt	1,971	2,021
Subordinated debt held by unconsolidated subsidiary trusts	$ 122,820	$ 122,814