Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - Level 3 [Member] - USD ($) $ in Thousands	1 Months Ended		2 Months Ended		3 Months Ended		8 Months Ended		9 Months Ended
	Sep. 30, 2020		Aug. 31, 2020		Sep. 30, 2019		Aug. 31, 2020		Sep. 30, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period	$ 0		$ 843		$ 3,945		$ 1,204		$ 10,630
Included in earnings	0	[1],[2]	(405)	[1]	2,393	[1]	872	[2]	(980)	[2]
Settlements	0		(437)		(3,627)		(2,075)		(6,939)
End of period	0		0		2,711		0		2,711
Total earnings (losses) for the period included in earnings attributable to the change in unrealized gain (loss) relating to assets still held at end of period	$ 0		$ (843)		$ (1,234)		$ (1,204)		$ (7,919)

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

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