Revenue Recognition - Narrative (Details) $ in Millions	6 Months Ended
	Mar. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Oct. 01, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Number of operating segments | segment	2
Contract with customer, liability, revenue recognized	$ 185.0
Retained earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Adoption of accounting standard		$ 0.0	$ 6.1	$ 6.1	$ 0.0	$ 0.0