INTANGIBLE ASSETS (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 23.1	$ 22.2	$ 15.5
Forecast of amortization expense associated with existing intangible assets for the years indicated:
2017	18.5
2018	13.8
2019	13.8
2020	13.8
2021	$ 13.8
Contributions In Aid of Construction [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	25 years
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, useful life (in years)	3 years