GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Identifiable Intangible Assets [Abstract]
Gross carrying amount	$ 151,718	$ 150,518
Accumulated amortization	(80,802)	(76,672)
Net carrying amount	70,916	73,846
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Apr - Dec 2019	11,433
2020	12,956
2021	11,053
2022	9,483
2023	7,947
Thereafter	18,044
Net carrying amount	70,916	73,846
Components of goodwill [Abstract]
Goodwill, beginning of period	738,327
Goodwill, activity	0
Goodwill, end of period	738,327
Accumulated impairment, beginning of period	(4,824)
Accumulated impairment, activity	0
Accumulated impairment, end of period	(4,824)
Goodwill, net, beginning of period	733,503
Goodwill, net, activity	0
Goodwill, net, end of period	733,503
Core Deposit Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	62,902	62,902
Accumulated amortization	(45,789)	(44,306)
Net carrying amount	17,113	18,596
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	17,113	18,596
Other Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	88,816	87,616
Accumulated amortization	(35,013)	(32,366)
Net carrying amount	53,803	55,250
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	$ 53,803	$ 55,250