DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of Fair Value of Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2025	Sep. 30, 2025
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 5.4	$ 7.9
Liability Derivatives	6.7	8.7
Commodity Contract
Derivatives, Fair Value [Line Items]
Netting of contracts in a receivable position against contracts in payable position	5.3	7.8
Commodity Contract \| Derivatives Designated as Hedging Instruments \| Other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	5.3	6.2
Commodity Contract \| Derivatives Designated as Hedging Instruments \| Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	6.6	7.1
Commodity Contract \| Derivatives Designated as Hedging Instruments \| Other assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.1	1.7
Commodity Contract \| Derivatives Designated as Hedging Instruments \| Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0.1	$ 1.6

COMPASS MINERALS INTERNATIONAL INC 10-Q