INCOME TAXES - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Jul. 31, 2014 MW	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($) photovoltaic_facility MW	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Equity Method Investments [Line Items]
Net tax benefit from share-based transactions										$ 1.9	$ 1.7
Unrecognized tax benefits		$ 0.1								0.1
Income tax benefit		(1.0)	$ (1.0)	$ (0.3)	$ (0.3)	$ (7.0)	$ (6.1)	$ (8.2)	$ (15.0)	(2.6)	(36.3)	$ (4.1)
Non-cash reduction in equity method investments		5.7	1.9	1.9	$ 0.0					9.8	2.6	$ 14.7
Waihonu
Schedule of Equity Method Investments [Line Items]
Non-cash reduction in equity method investments				8.7						8.7	0.0
Investment Tax Credit			$ 2.9	8.7
Total equity required for projects				$ 15.4
Number of photovoltaic facilities constructing | photovoltaic_facility				2
Facilities, power capacity (in megawatts) | MW				6.5
KRS II
Schedule of Equity Method Investments [Line Items]
Non-cash reduction in equity method investments										1.1	$ 2.6
Facilities, power capacity (in megawatts) | MW	12
Domestic Tax Authority
Schedule of Equity Method Investments [Line Items]
Tax credit carryforwards		6.2								6.2
State and Local Jurisdiction
Schedule of Equity Method Investments [Line Items]
Tax credit carryforwards		$ 6.9								$ 6.9