Property, Plant and Equipment - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Property, Plant and Equipment [Line Items]
Carrying value property, plant and equipment, net		$ 296.0		$ 316.1
Land under purchase options not yet recorded		10.8
Gain related to capital expenditures incurred to date		0.4	$ (0.1)
Montgomery Lease
Property, Plant and Equipment [Line Items]
Gain related to capital expenditures incurred to date	$ 0.2		$ 2.7
Closed Facilities | U.S.
Property, Plant and Equipment [Line Items]
Carrying value property, plant and equipment, net		$ 1.1		$ 1.1