Summary of Significant Accounting Policies - COGS (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Selling, general and administrative expenses
Cost of Goods Sold
Storage and other warehousing costs	$ 17.4	$ 13.7	$ 11.8