Fair Value Of Financial Instruments (Schedule Of Impact On Carrying Value Of Cell C Investment) (Details) $ in Thousands	Dec. 31, 2020 USD ($)
1.0% 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 based on 2% change	$ 0
1.0% Increase [Member] | EBITDA Multiple [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sensitivity for fair value of investment, increase (decrease) in valuation based on 2% change	627
1% 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 based on 2% change	1,514
1% Decrease [Member] | EBITDA Multiple [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Sensitivity for fair value of investment, increase (decrease) in valuation based on 2% change	$ 0