Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue
Net Sales	$ 282.1	$ 257.5	$ 564.5	$ 501.5
Shakes and other beverages
Disaggregation of Revenue
Net Sales	227.4	211.4	461.6	411.2
Powders
Disaggregation of Revenue
Net Sales	41.4	30.6	76.8	59.6
Nutrition bars
Disaggregation of Revenue
Net Sales	11.1	13.0	22.7	26.9
Other
Disaggregation of Revenue
Net Sales	$ 2.2	$ 2.5	$ 3.4	$ 3.8