Equity-Accounted Investments And Other Long-Term Assets (Summary Of Contractual Maturity Of Investment) (Details) $ in Thousands	Mar. 31, 2020 USD ($)
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	[1]
Due after ten years, Cost basis	0
Due after ten years, Cost basis	0
Total, Cost basis	0
Due in one year or less, Estimated fair value	0	[2]
Estimated fair value, Due in one year through five years	0	[1],[2]
Due in five years through ten years, Estimated fair value	0	[2]
Due after ten years, Estimated fair value	0	[2]
Total. Estimated fair value	$ 0	[2]

[1] The cost basis is zero ($0.0 million).

[2] The estimated fair value of the Cedar Cellular note has been calculated utilizing the Company’s portion of the security provided to the Company by Cedar Cellular, namely, Cedar Cellular’s investment in Cell C.