Financial Instruments and Risk Management - Narrative (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) Contract derivative_instrument	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($) Contract derivative_instrument	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 22, 2024 USD ($)	Sep. 30, 2023 USD ($)	Feb. 22, 2023	Jan. 22, 2021 USD ($)
Derivative [Line Items]
Unrecognized pre-tax loss			$ 62,700,000		$ (79,800,000)
Portion or pre-tax gain included in AOCI expected to be included in earnings	$ 600,000		600,000
Gain (Loss) Recognized in Income	0	$ 0	1,000,000.0	$ 0
Scenario, Forecast
Derivative [Line Items]
Notional value						$ 100,000,000.0
Interest Rate Contracts
Derivative [Line Items]
Notional value	700,000,000.0		700,000,000.0						$ 700,000,000.0
Interest Rate Contracts | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Derivative [Line Items]
Fixed interest rate								1.042%
Line of Credit | Senior Secured Term Loan B Facility, net of discount, due 2022
Derivative [Line Items]
Face amount of debt	841,000,000.0		841,000,000.0
Estimate of Fair Value
Derivative [Line Items]
Fair market value of fixed rate long-term debt	2,175,200,000		2,175,200,000				$ 2,000,900,000
Reported Value Measurement
Derivative [Line Items]
Fair market value of fixed rate long-term debt	2,376,400,000		2,376,400,000				2,362,200,000
Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Derivatives - Foreign Currency contracts	62,800,000		62,800,000				82,400,000
Designated as Hedging Instrument | Cash Flow Hedging | Zinc contracts
Derivative [Line Items]
Derivatives - Foreign Currency contracts	$ (500,000)		$ (500,000)				(700,000)
Derivative, Number of Open Contracts | Contract	19		19
Notional value	$ 29,000,000		$ 29,000,000
Designated as Hedging Instrument | Cash Flow Hedging | Foreign currency contracts
Derivative [Line Items]
Derivatives - Foreign Currency contracts	600,000		600,000				3,300,000
Notional value	$ 166,000,000		$ 166,000,000
Number of open contracts | derivative_instrument	64		64
Not Designated as Hedging Instrument | Foreign currency contracts
Derivative [Line Items]
Derivatives - Foreign Currency contracts	$ (500,000)		$ (500,000)				$ (1,300,000)
Gain (Loss) Recognized in Income	(2,700,000)	$ 100,000	500,000	$ 600,000
Not Designated as Hedging Instrument | Foreign currency contracts
Derivative [Line Items]
Notional value	$ 78,000,000		$ 78,000,000
Number of open contracts | derivative_instrument	3		3