Fair-Value Measurements (Placement Of Assets And Liabilities Within The Fair Value Hierarchy Levels) (Details) - Fair Value, Measurements, Recurring [Member] - Commodity Derivatives [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Fair Value	$ 1,908	$ 3,764
Liabilities Fair Value	(2,198)	(11,278)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Fair Value	0	0
Liabilities Fair Value	0	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Fair Value	0	0
Liabilities Fair Value	$ 0	$ 0