Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ (206)	$ (7,122)
Included in earnings	[1]	4,159	7,791
Settlements		6,677	(875)
End of period		10,630	(206)
Total gains for the period included in earnings attributable to the change in unrealized loss relating to assets still held at end of period		$ 10,836	$ 6,916

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