GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Identifiable Intangible Assets [Abstract]
Gross carrying amount	$ 155,741	$ 155,741
Accumulated amortization	(96,295)	(92,628)
Net carrying amount	59,446	63,113
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Apr - Dec 2020	10,133
2021	11,786
2022	10,105
2023	8,457
2024	7,041
Thereafter	11,924
Net carrying amount	59,446	63,113
Components of goodwill [Abstract]
Goodwill, beginning of period	778,634
Goodwill, activity	(337)
Goodwill, end of period	778,297
Accumulated impairment, beginning of period	(4,824)
Accumulated impairment, activity	0
Accumulated impairment, end of period	(4,824)
Goodwill, net, beginning of period	773,810
Goodwill, net, activity	(337)
Goodwill, net, end of period	773,473
Core Deposit Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	66,475	66,475
Accumulated amortization	(51,474)	(50,057)
Net carrying amount	15,001	16,418
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	15,001	16,418
Other Intangibles [Member]
Identifiable Intangible Assets [Abstract]
Gross carrying amount	89,266	89,266
Accumulated amortization	(44,821)	(42,571)
Net carrying amount	44,445	46,695
Estimated aggregate amortization expense for each of five succeeding fiscal years [Abstract]
Net carrying amount	$ 44,445	$ 46,695

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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-Name Accounting Standards Codification
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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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