Derivative Instruments and Hedging Activities - Effect of Derivative Instruments on the Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Effect of derivative instruments on the Consolidated Balance Sheet
Derivative Assets	$ 12,930	$ 2,991
Derivative Liabilities	2,688	40,259
Other current assets | Derivatives Not Designated as Hedges | Commodity contracts
Effect of derivative instruments on the Consolidated Balance Sheet
Derivative Assets	7,708	0
Derivative Liabilities	0	0
Other assets (non-current) | Derivatives Not Designated as Hedges | Commodity contracts
Effect of derivative instruments on the Consolidated Balance Sheet
Derivative Assets	5,222	2,991
Derivative Liabilities	0	0
Derivative instruments (current) | Derivatives Not Designated as Hedges | Commodity contracts
Effect of derivative instruments on the Consolidated Balance Sheet
Derivative Assets	0	0
Derivative Liabilities	$ 2,688	$ 40,259