DERIVATIVE COMMODITY INSTRUMENTS - Offsetting of Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Liabilities
Total derivatives	$ (68,423)	$ 56,504
Current Assets
Assets
Gross Amounts Recognized at Fair Value	1,756	72,563
Gross Amounts Offset in the Balance Sheets		(15,600)
Gross Amounts Offset in the Balance Sheets	(1,706)
Net Amount Presented in the Balance Sheets	50	56,963
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Fair Value Presented in the Balance Sheets	50	56,963
Current Liabilities
Liabilities
Gross Amounts Recognized at Fair Value	67,173	16,059
Gross Amounts Offset in the Balance Sheets		(15,600)
Gross Amounts Offset in the Balance Sheets	(1,706)
Net Amount Presented in the Balance Sheets	65,467	459
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Fair Value Presented in the Balance Sheets	65,467	$ 459
Noncurrent Liabilities
Liabilities
Gross Amounts Recognized at Fair Value	3,006
Gross Amounts Offset in the Balance Sheets	0
Net Amount Presented in the Balance Sheets	3,006
Financial Instruments	0
Cash Collateral Received	0
Net Fair Value Presented in the Balance Sheets	$ 3,006