Fair Value Of Financial Instruments (Narrative) (Details) R in Millions	3 Months Ended				6 Months Ended		9 Months Ended
	Mar. 31, 2019 ZAR (R) shares	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2019 ZAR (R) shares	Mar. 31, 2019 USD ($)	Mar. 31, 2019 USD ($) shares	Jun. 30, 2018 ZAR (R) contract	Jun. 30, 2018 USD ($) contract
Derivatives, Fair Value [Line Items]
Transfers into or out of Level 3 | $			$ 0	$ 0	$ 0	$ 0
Minimum [Member]
Derivatives, Fair Value [Line Items]
Years of significant fluctuation of US Dollar to ZAR exchange rate							3 years	3 years
Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Outstanding foreign exchange contracts | contract										0	0
Cell C [Member]
Derivatives, Fair Value [Line Items]
Equity method investment, percentage of ownership interest	15.00%						15.00%		15.00%
Adjusted EBITDA	R 3,500.0						R 3,500.0		$ 242,600,000	R 3,900.0	$ 284,800,000
Net external debt	R 9,400.0						R 9,400.0		$ 648,900,000	R 8,800.0	$ 641,100,000
EBITDA multiple	6.40%						6.40%		6.40%	6.75%	6.75%
Marketability discount	10.00%						10.00%		10.00%
Cell C [Member] | EBITDA Multiple [Member]
Derivatives, Fair Value [Line Items]
Impact of increase and decrease to EBITDA multiple | $									0.50
Finbond [Member]
Derivatives, Fair Value [Line Items]
Investment shares owned | shares	267,672,032						267,672,032		267,672,032
Cell C [Member] | Net1 SA [Member] | Class A [Member]
Derivatives, Fair Value [Line Items]
Investment shares owned | shares	75,000,000						75,000,000		75,000,000
DNI [Member]
Derivatives, Fair Value [Line Items]
DNI contingent consideration	R 400.0						R 400.0		$ 27,600,000
Long-term liabilities										R 373.6	$ 27,200,000
Settlement of contingent consideration | R							400.0
Accretion of interest	R 14.4	$ 1,000,000					R 26.4	$ 1,800,000