INCOME TAXES Income Tax Disclosure (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Jan. 31, 2016
Business Acquisition [Line Items]
Decrease to deferred tax assets	$ (48.0)
Release of valuation allowance	$ (48.0)
San Juan Coal Company
Business Acquisition [Line Items]
Deferred tax liabilities		$ 48.0