GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Identifiable Intangible Assets [Abstract]
Gross carrying amount	$ 150,518	$ 149,437
Accumulated amortization	(72,297)	(58,779)
Net carrying amount	78,221	90,658
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Oct - Dec 2018	4,375
2019	15,296
2020	12,722
2021	10,853
2022	9,317
Thereafter	25,658
Net carrying amount	78,221	90,658
Components of goodwill [Abstract]
Goodwill, beginning of period	739,254
Goodwill, activity	(951)
Goodwill, end of period	738,303
Accumulated impairment, beginning of period	(4,824)
Accumulated impairment, activity	0
Accumulated impairment, end of period	(4,824)
Goodwill, net, beginning of period	734,430
Goodwill, net, activity	(951)
Goodwill, net, end of period	733,479
Core Deposit Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	62,902	62,902
Accumulated amortization	(42,790)	(37,877)
Net carrying amount	20,112	25,025
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	20,112	25,025
Other Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	87,616	86,535
Accumulated amortization	(29,507)	(20,902)
Net carrying amount	58,109	65,633
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	$ 58,109	$ 65,633