Accumulated Other Comprehensive Income (Loss) Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (28.3)		$ (28.3)		$ (24.5)
Other comprehensive loss	(1.6)	$ 0.7	(3.8)	$ (0.2)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(25.3)		(25.3)		(21.5)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(3.8)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(3.0)		(3.0)		(3.0)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (28.3)		(28.3)		$ (24.5)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(3.8)
Other comprehensive loss			$ (3.8)