Fair Value Measurements (Reconciliations Of Level 3 Fair Value Measurements) (Details) - USD ($) $ in Thousands	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2020	Aug. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Beginning of period	$ 0	$ 1,204	$ 10,630
Included in earnings	0	978	(1,494)
Settlements	0	(2,182)	(7,932)
End of period	0	0	1,204
Total gains (losses) for the period included in earnings attributable to the change in unrealized loss relating to assets still held at end of period	$ 0	$ (1,204)	$ (9,426)