Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue
Net sales	$ 1,666.8	$ 1,371.5	$ 1,247.1
Revenue Benchmark | Geographic Concentration Risk | Non-US
Disaggregation of Revenue
Percentage of net sales	10.50%	11.30%	11.70%
Revenue Benchmark | Geographic Concentration Risk | Europe as a percentage of Non-US
Disaggregation of Revenue
Percentage of net sales			34.10%
Revenue Benchmark | Geographic Concentration Risk | Canada as a percentage of Non-US
Disaggregation of Revenue
Percentage of net sales	40.80%	35.40%
Revenue Benchmark | Customer Concentration Risk | One customer
Disaggregation of Revenue
Percentage of net sales	33.90%	31.90%	31.50%
Revenue Benchmark | Customer Concentration Risk | The second customer
Disaggregation of Revenue
Percentage of net sales	30.00%	31.60%	33.80%
Revenue Benchmark | Customer Concentration Risk | The third customer
Disaggregation of Revenue
Percentage of net sales	11.40%
Shakes and other beverages
Disaggregation of Revenue
Net sales	$ 1,327.0	$ 1,084.0	$ 1,014.2
Powders
Disaggregation of Revenue
Net sales	289.7	242.2	178.6
Other Products
Disaggregation of Revenue
Net sales	$ 50.1	$ 45.3	$ 54.3