Derivatives (Details 2) (Sales, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on commodity derivatives included in sales and merchandising revenues	$ 73,517	$ 31,068	$ 19,831	$ 67,436