Equity-Accounted Investments And Other Long-Term Assets (Summary Of Unrealized Gain (Loss) On Investments) (Details) $ in Thousands	Jun. 30, 2018 USD ($)
Schedule Of Equity And Held To Maturity Investments [Line Items]
Cost basis	$ 154,714
Unrealized holding gains	33,868
Carrying value	183,343
Cell C [Member]
Schedule Of Equity And Held To Maturity Investments [Line Items]
Cost basis	145,714
Unrealized holding gains	32,473
Carrying value	172,948
Cedar Cellular [Member]
Schedule Of Equity And Held To Maturity Investments [Line Items]
Cost basis	9,000
Unrealized holding gains	1,395
Carrying value	$ 10,395