DERIVATIVE INSTRUMENTS - Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Assets	$ 2,562	$ 1,141
Liabilities	13,695	13,471
Commodity Contract
Derivatives, Fair Value [Line Items]
Assets	2,562	1,141
Liabilities	0	0
Derivatives not designated as hedging instruments under GAAP
Derivatives, Fair Value [Line Items]
Assets	2,562	1,141
Liabilities	13,695	13,471
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives – Energy Related – Current
Derivatives, Fair Value [Line Items]
Assets	2,281	1,077
Liabilities	3,276	5,489
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives – Energy Related – Non-Current
Derivatives, Fair Value [Line Items]
Assets	281	64
Liabilities	73	351
Derivatives not designated as hedging instruments under GAAP | Interest Rate Contract | Derivatives – Other Current
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	535	0
Derivatives not designated as hedging instruments under GAAP | Interest Rate Contract | Derivatives – Other Noncurrent
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	$ 9,811	$ 7,631