Derivatives (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gains on commodity derivatives included in sales and merchandising revenues	$ 0	$ 0	$ 67,579
Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Gains on commodity derivatives included in sales and merchandising revenues	$ (15,012)	$ 62,541	$ 0