Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - Level 3 [Member] - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ (206)	$ (7,122)
Included in earnings	[1]	(3,919)	5,903
Settlements		919	617
End of period		(3,206)	(602)
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		$ (3,000)	$ 6,520

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