SUMMARY OF SIGNIFCANT ACCOUNTING POLICIES - Depreciation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciation	$ 12.0	$ 39.8	$ 18.7
Plants and facilities
Property, Plant and Equipment [Line Items]
Estimated useful life		30 years	30 years
Pipelines
Property, Plant and Equipment [Line Items]
Estimated useful life		40 years	40 years
Power Generator
Property, Plant and Equipment [Line Items]
Estimated useful life	12 years