Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - Level 3 [Member] - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ 1,204	$ 10,630
Included in earnings	[1]	563	(5,434)
Settlements		(819)	(2,116)
End of period		948	3,080
Total losses for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period		$ (256)	$ (7,550)

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