Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosures [Line Items]
Deferred tax assets related to operating loss carryforwards in foreign jurisdictions	$ 68.6
Deferred tax assets related to domestic federal net operating loss carryforwards	1.8
Deferred tax assets related to state net operating loss carryforwards	0.3
Deferred tax assets related to state credits	15.0
Deferred tax assets related to credits in foreign jurisdictions	8.3
Capital loss carryforwards	3.8
Valuation allowances on deferred tax assets	58.2	$ 26.9
Impact of tax holidays	$ 3.6	$ 4.1	$ 4.3
Benefit of tax holidays on net income per share (diluted) (usd per share)	$ 0.05	$ 0.06	$ 0.07
Undistributed earnings in our non-U.S. subsidiaries	$ 335.9
Total gross unrecognized tax benefits	4.5	$ 5.1	$ 5.8	$ 4.1
Unrecognized tax benefits that would impact effective tax rate, if recognized	3.3	3.6	3.3
Accrued interest and penalties related to unrecognized tax benefits	2.6	3.0	3.0
Income tax benefit for interest and penalties	0.4	$ 0.0	$ 0.2
Minimum [Member]
Income Tax Disclosures [Line Items]
Amount of reasonably possible decrease	0.5
Maximum [Member]
Income Tax Disclosures [Line Items]
Amount of reasonably possible decrease	$ 1.0