GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Identifiable Intangible Assets [Abstract]
Gross carrying amount	$ 159,865	$ 155,741
Accumulated amortization	(99,819)	(92,628)
Net carrying amount	60,046	63,113
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Jul - Dec 2020	7,106
2021	12,640
2022	10,844
2023	9,082
2024	7,551
Thereafter	12,823
Net carrying amount	60,046	63,113
Components of goodwill [Abstract]
Goodwill, net, beginning of period	773,810
Goodwill, net, activity	18,905
Goodwill, net, end of period	792,715
Core Deposit Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	69,403	66,475
Accumulated amortization	(52,838)	(50,057)
Net carrying amount	16,565	16,418
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	16,565	16,418
Other Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	90,462	89,266
Accumulated amortization	(46,981)	(42,571)
Net carrying amount	43,481	46,695
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	$ 43,481	$ 46,695