Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ 9,094	$ 3,355
Included in earnings	[1]	(9,042)	15,260
Settlements		(7,174)	(9,521)
End of period		(7,122)	9,094
Total gains for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period		$ (16,216)	$ 5,739

[1] Commodity derivatives are reported in the Consolidated Statements of Operations in gain (loss) on derivatives.