Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - Level 3 [Member] - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning of period		$ (3,206)	$ (602)	$ (206)	$ (7,122)
Included in earnings	[1]	(4,704)	5,214	(8,624)	11,117
Settlements		1,775	(519)	2,695	98
End of period		(6,135)	4,093	(6,135)	4,093
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		$ (2,929)	$ 4,695	$ (5,929)	$ 11,215

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