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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ (6,135)	$ 4,093	$ (206)	$ (7,122)
Included in earnings	[1]	(3,700)	(2,015)	(12,324)	9,102
Settlements		2,316	(592)	5,011	(494)
End of period		(7,519)	1,486	(7,519)	1,486
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		$ (1,384)	$ (2,607)	$ (7,313)	$ 8,608

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