v3.26.1
FAIR VALUE MEASUREMENTS
 9 Months Ended
Jun. 30, 2026
Fair Value Disclosures [Abstract]  
FAIR VALUE MEASUREMENTS FAIR VALUE MEASUREMENTS
The Company’s financial instruments are measured and reported at their estimated fair values. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction. When available, the Company uses quoted prices in active markets to determine the fair values for its financial instruments (Level 1 inputs) or, absent quoted market prices, observable market-corroborated inputs over the term of the financial instruments (Level 2 inputs). The Company does not have any unobservable inputs that are not corroborated by market inputs (Level 3 inputs).
 
Recurring Fair Value Measurements

The following tables summarizes the fair value hierarchy for each type of instrument carried at fair value on a recurring basis (in millions):
Fair Value Measurements at June 30, 2026 Using
Total Carrying Value at
June 30, 2026
Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)(b)
$4.1 $4.1 $— $— 
Derivatives – natural gas instruments, net4.7 — 4.7 — 
Total assets at fair value$8.8 $4.1 $4.7 $— 
Liability Class:
Liabilities related to non-qualified savings plan$4.1 $4.1 $— $— 
Derivatives – natural gas instruments, net5.9 — 5.9 — 
Total liabilities at fair value$10.0 $4.1 $5.9 $— 
(a)Includes mutual fund investments of approximately 37% in common stock of large-cap U.S. companies, 4% in common stock of small to mid-cap U.S. companies, 1% in the common stock of international companies, 9% in bond funds, 12% in short-term investments, and 37% in blended funds.
(b)The investments related to a non-qualified deferred compensation arrangement on behalf of certain members of management. The Company has a liability for the related-party transaction recorded on Other noncurrent liabilities for deferred compensation obligation.
    
Fair Value Measurements at September 30, 2025 Using
Total Carrying Value at
September 30, 2025		Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)(b)
$3.5 $3.5 $— $— 
Derivatives – natural gas instruments, net7.9 — 7.9 — 
Total assets at fair value$11.4 $3.5 $7.9 $— 
Liability Class:
Liabilities related to non-qualified savings plan$3.5 $3.5 $— $— 
Derivatives – natural gas instruments, net8.7 — 8.7 — 
Total liabilities at fair value$12.2 $3.5 $8.7 $— 
(a)Includes mutual fund investments of approximately 29% in common stock of large-cap U.S. companies, 4% in common stock of small to mid-cap U.S. companies, 2% in the common stock of international companies, 9% in bond funds, 20% in short-term investments, and 36% in blended funds.
(b)The investments related to a non-qualified deferred compensation arrangement on behalf of certain members of management. The Company has a liability for the related-party transaction recorded on Other noncurrent liabilities for deferred compensation obligation.

Valuation Techniques: The Company holds marketable securities associated with its deferred contribution and pre-tax savings plans, which are valued based on readily available quoted market prices. The Company utilizes derivative instruments to manage its risk of changes in natural gas prices and foreign exchange rates (see Note 11. Derivative Financial Instruments). The fair values of the natural gas and foreign currency derivative instruments are determined using market data of forward prices for all of the Company’s contracts. 
Other Fair Value Measurements

The Company is required to disclose the fair value of financial instruments that are not recognized at fair value in the statement of financial position for which it is practicable to estimate that value (in millions):

Fair Value Measurements at June 30, 2026 Using
Total Carrying Value at
June 30, 2026
Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
8.00% Senior Notes due July 2030
$650.0 $— $684.2 $— 

Fair Value Measurements at September 30, 2025 Using
Total Carrying Value at
September 30, 2025		Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
8.00% Senior Notes due July 2030
$650.0 $— $680.1 $— 
6.75% Senior Notes due December 2027
150.0 — 150.1 — 
Valuation Techniques: Observable market-based inputs were used to estimate fair value for Level 2 inputs, based on available trading information. Cash and cash equivalents, receivables (net of allowance for doubtful accounts) and accounts payable are carried at cost, which approximates fair value due to their liquid and short-term nature.