GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jul. 01, 2018	Dec. 31, 2016
Goodwill [Line Items]
Goodwill	$ 734,607,000	$ 3,578,000	$ 731,029,000	$ 4,838,000
Impairment of goodwill	0	1,260,000
Intangible assets	28,100,000	12,500,000
Impairment of intangible assets	0	$ 2,200,000
ETG Utility Operations
Goodwill [Line Items]
Goodwill	730,900,000
On-site Energy Production
Goodwill [Line Items]
Goodwill	3,600,000
ELK Utility Operations
Goodwill [Line Items]
Goodwill	$ 100,000
Minimum
Goodwill [Line Items]
Finite lived useful life	2 years
Maximum
Goodwill [Line Items]
Finite lived useful life	20 years