Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue
Net Sales	$ 2,316.6	$ 1,996.2	$ 1,666.8
Revenue Benchmark | Geographic Concentration Risk | Non-US
Disaggregation of Revenue
Percentage of net sales	11.90%	10.80%	10.50%
Revenue Benchmark | Geographic Concentration Risk | Canada as a percentage of Non-US
Disaggregation of Revenue
Percentage of net sales	35.60%	37.70%	40.80%
Revenue Benchmark | Customer Concentration Risk | One customer
Disaggregation of Revenue
Percentage of net sales	34.30%	35.80%	33.90%
Revenue Benchmark | Customer Concentration Risk | The second customer
Disaggregation of Revenue
Percentage of net sales	27.50%	27.30%	30.00%
Revenue Benchmark | Customer Concentration Risk | The third customer
Disaggregation of Revenue
Percentage of net sales	12.20%	11.70%	11.40%
Shakes and other beverages
Disaggregation of Revenue
Net Sales	$ 1,892.9	$ 1,618.8	$ 1,320.2
Powders
Disaggregation of Revenue
Net Sales	366.5	326.7	289.7
Other Products
Disaggregation of Revenue
Net Sales	$ 57.2	$ 50.7	$ 56.9