GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS - Narrative (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 702,070,000			$ 702,070,000		$ 702,070,000
Amortization expense	1,300,000		$ 1,500,000	2,600,000	$ 3,000,000.0
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
Goodwill	700,200,000			$ 700,200,000		700,200,000
Corporate and Other
Goodwill [Line Items]
Goodwill	$ 1,900,000			$ 1,900,000		$ 1,900,000