Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue
Net sales	$ 1,996.2	$ 1,666.8	$ 1,371.5
Revenue Benchmark | Geographic Concentration Risk | Non-US
Disaggregation of Revenue
Percentage of net sales	10.80%	10.50%	11.30%
Revenue Benchmark | Geographic Concentration Risk | Canada as a percentage of Non-US
Disaggregation of Revenue
Percentage of net sales	37.70%	40.80%	35.40%
Revenue Benchmark | Customer Concentration Risk | One customer
Disaggregation of Revenue
Percentage of net sales	35.80%	33.90%	31.90%
Revenue Benchmark | Customer Concentration Risk | The second customer
Disaggregation of Revenue
Percentage of net sales	27.30%	30.00%	31.60%
Revenue Benchmark | Customer Concentration Risk | The third customer
Disaggregation of Revenue
Percentage of net sales	11.70%	11.40%
Shakes and other beverages
Disaggregation of Revenue
Net sales	$ 1,619.2	$ 1,327.0	$ 1,084.0
Powders
Disaggregation of Revenue
Net sales	326.7	289.7	242.2
Other Products
Disaggregation of Revenue
Net sales	$ 50.3	$ 50.1	$ 45.3