Derivatives (Effects on Consolidated Statements of Operations And Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives, amount of gain (loss) recognized in income	$ (19,042)	$ 14,925	$ 35,468
Commodity Derivatives [Member] | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives, amount of gain (loss) recognized in income	(13,195)	(1,101)	0
Commodity Derivatives [Member] | Not Designated As Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives, amount of gain (loss) recognized in income	$ (5,847)	$ 16,026	$ 35,468