Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - Level 3 [Member] - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ 4,093	$ (4,761)	$ (7,122)	$ 9,094
Included in earnings	[1]	(2,015)	3,077	9,102	(3,257)
Settlements		(592)	(443)	(494)	(7,964)
End of period		1,486	(2,127)	1,486	(2,127)
Total gains (losses) for the period included in earnings attributable to the change in unrealized gain relating to assets still held at end of period		$ (2,607)	$ 2,634	$ 8,608	$ (11,221)

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