Fair Value Of Financial Instruments (Schedule Of Impact On Carrying Value Of Cell C Investment) (Details) $ in Thousands	Mar. 31, 2021 USD ($)
3.0% Increase [Member] | Weighted Average Cost of Capital (WACC) Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sensitivity for fair value of investment, increase (decrease) in valuation	$ 0
3.0% Increase [Member] | EBITDA Multiple [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sensitivity for fair value of investment, increase (decrease) in valuation	2,134
2.5% Decrease [Member] | Weighted Average Cost of Capital (WACC) Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sensitivity for fair value of investment, increase (decrease) in valuation	3,349
2.5% Decrease [Member] | EBITDA Multiple [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sensitivity for fair value of investment, increase (decrease) in valuation	$ 0