GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 706,960,000			$ 706,960,000		$ 702,070,000
Amortization expense	1,400,000		$ 1,500,000	4,000,000.0	$ 4,600,000
Impairment of intangible assets (excluding goodwill)	0		$ 0	$ 0	$ 0
Minimum
Goodwill [Line Items]
Useful life of finite-lived intangible assets				2 years
Maximum
Goodwill [Line Items]
Useful life of finite-lived intangible assets				20 years
ETG Utility Operations
Goodwill [Line Items]
Goodwill impairment	0	$ 0
Goodwill	700,200,000			$ 700,200,000		700,200,000
Corporate and Other
Goodwill [Line Items]
Goodwill	$ 6,800,000			$ 6,800,000		$ 1,900,000