Income Tax (Narrative) (Details) R in Millions, $ in Millions			3 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2018 USD ($)	Sep. 30, 2018 ZAR (R)	Sep. 30, 2018 USD ($)
Valuation Allowance [Line Items]
Effective tax rate			36.80%
Income tax rate	21.00%	35.00%
Provisional transition tax before foreign tax credits				$ 55.8
Transition tax liability after generated foreign tax credits				0.0
Valuation allowance related to net operating losses					R 223.4	$ 15.1
Unrecognized tax benefit				$ 0.8		0.9
Accrued interest related to uncertain tax positions						$ 0.1
Foreign Cash And Other Net Current Assets [Member]
Valuation Allowance [Line Items]
Effective tax rate				15.50%
Foreign Income [Member]
Valuation Allowance [Line Items]
Effective tax rate				8.00%