Equity-Accounted Investments And Other Long-Term Assets (Summary Of Contractual Maturity Of Investment) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Equity-Accounted Investments And Other Long-Term Assets [Abstract]
Due in one year or less, Cost basis		$ 0
Due in one year through five, Cost basis		0
Due after ten years, Cost basis	$ 0
Due in five years through ten years, Cost basis	0
Total, Cost basis	0
Due in one year or less, Estimated fair value	0
Estimated fair value, Due in one year through five years		$ 0
Due in five years through ten years, Estimated fair value	0
Due after ten years, Estimated fair value	0
Total. Estimated fair value	$ 0