Compass Minerals International (CMP) 10-Q 10 Feb 25 2025 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Dec. 31, 2024	Feb. 05, 2025
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Dec. 31, 2024
Document Transition Report	false
Entity File Number	001-31921
Entity Registrant Name	Compass Minerals International, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-3972986
Entity Address, Address Line One	9900 West 109th Street
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Overland Park
Entity Address, State or Province	KS
Entity Address, Postal Zip Code	66210
City Area Code	913
Local Phone Number	344-9200
Title of 12(b) Security	Common stock, $0.01 par value
Trading Symbol	CMP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		41,504,100
Entity Central Index Key	0001227654
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	Q1
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Current assets:
Cash and cash equivalents	$ 45.8	$ 20.2
Receivables, less allowance for doubtful accounts of $3.1 and $3.6 at December 31, 2024 and September 30, 2024, respectively	261.7	126.1
Inventories, less allowance of $14.5 and $11.4 at December 31, 2024 and September 30, 2024, respectively	367.1	414.1
Other current assets	23	26.9
Total current assets	697.6	587.3
Property, plant and equipment, net	778.6	806.5
Intangible assets, net	80.1	82.5
Goodwill	5.8	6
Other noncurrent assets	158.8	157.8
Total assets	1,720.9	1,640.1
Current liabilities:
Current portion of long-term debt	8.7	7.5
Accounts payable	96.2	82.1
Accrued salaries and wages	15.5	22.6
Income taxes payable	6	13.1
Accrued interest	6	13.3
Accrued expenses and other current liabilities	162.4	78.4
Total current liabilities	294.8	217
Long-term debt, net of current portion	965.7	910
Deferred income taxes, net	56	56.5
Other noncurrent liabilities	141.4	140
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock: $0.01 par value, 200,000,000 authorized shares; 42,197,964 issued shares at December 31, 2024 and September 30, 2024	0.4	0.4
Additional paid-in capital	424.3	420.6
Treasury stock, at cost — 732,721 shares at December 31, 2024 and 816,013 shares at September 30, 2024	(10.4)	(10.2)
Retained (loss) earnings	(21.4)	2.2
Accumulated other comprehensive loss	(129.9)	(96.4)
Total stockholders’ equity	263	316.6
Total liabilities and stockholders’ equity	$ 1,720.9	$ 1,640.1

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
ASSETS
Allowance for doubtful accounts	$ 3.1	$ 3.6
Inventory Valuation Reserves	$ 14.5	$ 11.4
Stockholders’ equity:
Common stock, par or stated value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	42,197,964	42,197,964
Treasury stock, shares (in shares)	732,721	816,013

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Sales	$ 307.2	$ 341.7
Gross profit	34.3	71.1
Selling, general and administrative expenses	33.3	45.7
Loss on impairments	0	74.8
Other operating expense	0.5	4.2
Operating earnings (loss)	0.5	(53.6)
Other (income) expense:
Interest income	(0.4)	(0.4)
Interest expense	16.9	15.9
(Gain) loss on foreign exchange	(5.2)	1.9
Other expense, net	3.1	0.7
Loss before income taxes	(13.9)	(71.7)
Income tax expense	9.7	3.6
Net loss	$ (23.6)	$ (75.3)
Basic net (loss) earnings per common share (in dollars per share)	$ (0.57)	$ (1.83)
Diluted net (loss) earnings per common share (in dollars per share)	$ (0.57)	$ (1.83)
Weighted-average common shares outstanding (in thousands):
Basic (in shares)	41,441	41,205
Diluted (in shares)	41,441	41,205
Shipping and handling cost
Cost	$ 80.6	$ 91.3
Product cost
Cost	$ 192.3	$ 179.3

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (23.6)	$ (75.3)
Other comprehensive income (loss):
Unrealized gain from change in pension obligations, net of tax of $(0.1) for the three months ended December 31, 2024 and 2023, respectively	0.2	0.2
Unrealized loss from change in other postretirement benefits, net of tax of $0.0 for the three months ended December 31, 2024 and 2023	(0.1)	0
Unrealized loss on cash flow hedges, net of tax of $0.0 for the three months ended December 31, 2024 and 2023, respectively	(0.3)	(1.8)
Cumulative translation adjustment	(33.3)	14.6
Comprehensive loss	$ (57.1)	$ (62.3)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Statement of Comprehensive Income [Abstract]
Unrealized gain (loss) from change in pension obligations, tax	$ (0.1)	$ (0.1)
Unrealized loss, other postretirement benefits, tax	0	0
Unrealized income (loss) on cash flow hedges, tax	$ 0	$ 0

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings (Loss)	Accumulated Other Comprehensive Loss
Beginning balance at Sep. 30, 2023	$ 521	$ 0.4	$ 413.1		$ 220.9	$ (104.7)
Beginning balance, treasury stock at Sep. 30, 2023				$ (8.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive loss	(62.3)				(75.3)	13
Dividends on common stock	(6.4)				(6.4)
Shares issued for stock units, net of shares withheld for taxes	(0.8)		(0.2)	(0.6)
Stock-based compensation	11.9		11.9
Ending balance at Dec. 31, 2023	463.4	0.4	424.8		139.2	(91.7)
Ending balance, treasury stock at Dec. 31, 2023				(9.3)
Beginning balance at Sep. 30, 2024	316.6	0.4	420.6		2.2	(96.4)
Beginning balance, treasury stock at Sep. 30, 2024	(10.2)			(10.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive loss	(57.1)				(23.6)	(33.5)
Shares issued for stock units, net of shares withheld for taxes	(0.4)		(0.2)	(0.2)
Stock-based compensation	3.9		3.9
Ending balance at Dec. 31, 2024	263	$ 0.4	$ 424.3		$ (21.4)	$ (129.9)
Ending balance, treasury stock at Dec. 31, 2024	$ (10.4)			$ (10.4)

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical)	3 Months Ended
	Dec. 31, 2023 $ / shares
Statement of Stockholders' Equity [Abstract]
Cash dividends per share (in dollars per share)	$ 0.15

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities:
Net loss	$ (23.6)	$ (75.3)
Adjustments to reconcile net loss to net cash flows provided by operating activities:
Depreciation, depletion and amortization	26.8	25.5
Amortization of deferred financing costs	0.8	0.6
Stock-based compensation	3.9	11.9
Deferred income taxes	2.7	0.6
Unrealized foreign exchange (gain) loss	(5.7)	1.7
Loss on impairments	0	74.8
Other, net	(0.9)	1.5
Changes in operating assets and liabilities:
Receivables	(61.3)	(37.6)
Inventories	39.1	7.8
Other assets	(2)	4
Accounts payable and accrued expenses and other current liabilities	9.1	(65.4)
Other liabilities	7	(2.4)
Net cash used in operating activities	(4.1)	(52.3)
Cash flows from investing activities:
Capital expenditures	(21.8)	(48.6)
Other, net	(0.4)	(0.7)
Net cash used in investing activities	(22.2)	(49.3)
Cash flows from financing activities:
Proceeds from revolving credit facility borrowings	140.3	102.4
Principal payments on revolving credit facility borrowings	(100.8)	(31.5)
Proceeds from issuance of long-term debt	19.6	38.4
Principal payments on long-term debt	(1.6)	(1.2)
Dividends paid	0	(6.4)
Deferred financing costs	(2.4)	0
Shares withheld to satisfy employee tax obligations	(0.4)	(0.8)
Other, net	(1.6)	0
Net cash provided by financing activities	53.1	100.9
Effect of exchange rate changes on cash and cash equivalents	(1.2)	0.3
Net change in cash and cash equivalents	25.6	(0.4)
Cash and cash equivalents, beginning of the year	20.2	38.7
Cash and cash equivalents, end of period	45.8	38.3
Supplemental cash flow information:
Interest paid, net of amounts capitalized	23.4	23.6
Income taxes paid, net of refunds	8	12.8
Net change to property, plant and equipment through accounts payable and accrued expenses and other current liabilities	$ 9	$ 17.7

Accounting Policies and Basis o

Accounting Policies and Basis of Presentation	3 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Accounting Policies and Basis of Presentation	Accounting Policies and Basis of Presentation: Compass Minerals International, Inc. (“CMI”), through its subsidiaries (collectively, the “Company”), is a leading global provider of essential minerals focused on safely delivering where and when it matters to help solve nature’s challenges for customers and communities. The Company’s salt products help keep roadways safe during winter weather and are used in numerous other consumer, industrial, chemical and agricultural applications. Its plant nutrition business is the leading North American producer of sulfate of potash (“SOP”), which is used in the production of specialty fertilizers for high-value crops and turf and helps improve the quality and yield of crops, while supporting sustainable agriculture. The Company’s principal products are salt, consisting of sodium chloride and magnesium chloride, and SOP. The Company is also working to develop long-term fire-retardant solutions to help combat wildfires. The Company’s production sites are located in the United States (“U.S.”), Canada and the United Kingdom (“U.K.”). The Company also provides records management services in the U.K. Except where otherwise noted, references to North America include only the continental U.S. and Canada, and references to the U.K. include only England, Scotland and Wales. References to “Compass Minerals,” “our,” “us” and “we” refer to CMI and its consolidated subsidiaries. CMI is a holding company with no significant operations other than those of its wholly-owned subsidiaries. The consolidated financial statements include the accounts of CMI and its wholly-owned domestic and foreign subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete consolidated financial statements. These unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements of the Company for the annual period ended September 30, 2024, as filed with the Securities and Exchange Commission (the “SEC”) in its Annual Report on Form 10-K on December 16, 2024 (“2024 Form 10-K”). In the opinion of management, all adjustments, consisting of normal recurring adjustments considered necessary for a fair presentation, have been included. The Company experiences a substantial amount of seasonality in its sales, including its salt deicing product sales. Consequently, Salt segment sales and operating income are generally higher in the first and second fiscal quarters (ending December 31 and March 31) and lower during the third and fourth fiscal quarters (ending June 30 and September 30). In particular, sales of highway and consumer deicing salt and magnesium chloride products vary based on the severity of the winter conditions in areas where the products are used. Following industry practice in North America and the U.K., the Company seeks to stockpile sufficient quantities of deicing salt throughout the first, third and fourth fiscal quarters (ending December 31, June 30 and September 30) to meet the estimated requirements for the winter season. Production of deicing salt can also vary based on the severity or mildness of the preceding winter season. Due to the seasonal nature of the deicing product lines, operating results for the interim periods are not necessarily indicative of the results that may be expected for the full fiscal year. The Company’s plant nutrition business is also seasonal. As a result, the Company and its customers generally build inventories during the plant nutrition business’ low demand periods of the year (which are typically winter and summer, but can vary due to weather and other factors) to ensure timely product availability during the peak sales seasons (which are typically spring and autumn, but can also vary due to weather and other factors). Lastly, any expected results of the Company’s fire retardant business are also seasonal with peak demand for fire retardant products and services occurring from June through September. The Company does not yet have a contract for fiscal 2025. Significant Accounting Policies The Company’s significant accounting policies are detailed in “Note 2 – Summary of Significant Accounting Policies” within Part II, Item 8 of its 2024 Form 10-K. There were no material changes in the Company’s significant accounting policies from those described in its 2024 Form 10-K. Recent Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-07, “Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures”, which updates reportable segment disclosure requirements primarily to include enhanced disclosures about significant segment expenses. The amendments are effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied retrospectively to all prior periods presented in the financial statements. Management is currently evaluating this ASU to determine its impact on the Company's disclosures. In December 2023, the FASB issued ASU 2023-09, “Income Taxes (Topic 740): Improvements to Income Tax Disclosures”, which updates income tax disclosures by requiring consistent categories and additional disaggregation of information in the rate reconciliation and income taxes paid by jurisdiction. The amendments are effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied prospectively; however, retrospective application is permitted. Management is currently evaluating this ASU to determine its impact on the Company’s disclosures. In November 2024, the FASB issued amended guidance related to disclosure of disaggregated expenses (“ASU 2024-03”). This amendment requires public business entities to provide detailed disclosures in the notes to financial statements disaggregating specific expense categories, including employee compensation, depreciation, and intangible asset amortization, as well as certain other disclosures to provide enhanced transparency into the nature and function of expenses. This new guidance is effective for annual periods beginning in the Company’s fiscal 2028 and interim periods following annual adoption, with early adoption permitted. This guidance will be applied on a prospective basis with retrospective application permitted. Management is currently evaluating this ASU to determine its impact on the Company’s disclosures.

Revenues

Revenues	3 Months Ended
	Dec. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenues	Revenues: Deferred Revenue Deferred revenue represents collections under non-cancellable contracts before the related product or service is transferred to the customer. The portion of deferred revenue that is anticipated to be recognized as revenue during the succeeding twelve-month period is recorded in accrued expenses and other current liabilities on the Consolidated Balance Sheets. Deferred revenue as of both December 31, 2024 and September 30, 2024 was approximately $3.6 million. See Note 9 for a disaggregation of sales by segment, type and geographical region.

Inventories

Inventories	3 Months Ended
	Dec. 31, 2024
Inventory Disclosure [Abstract]
Inventories	Inventories: Inventories consist of the following (in millions): December 31, September 30, Finished goods $ 286.8 $ 336.5 Work in process 6.4 6.4 Raw materials and supplies (a) 73.9 71.2 Total inventories $ 367.1 $ 414.1 (a)

Property, Plant and Equipment,

Property, Plant and Equipment, Net	3 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment, Net	Property, Plant and Equipment, Net: Property, plant and equipment, net, consists of the following (in millions): December 31, September 30, Land, buildings and structures, and leasehold improvements $ 550.2 $ 559.8 Machinery and equipment 1,120.2 1,149.5 Office furniture and equipment 23.9 24.1 Mineral interests 166.5 170.4 Construction in progress 57.5 56.0 1,918.3 1,959.8 Less: accumulated depreciation and depletion (1,139.7) (1,153.3) Property, plant and equipment, net $ 778.6 $ 806.5

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets: Changes in the carrying amount of goodwill are summarized as follows (in millions): Corporate & Other Balance as of September 30, 2024 $ 6.0 Foreign currency translation adjustment (0.2) Balance as of December 31, 2024 $ 5.8

Income Taxes

Income Taxes	3 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes: The Company’s effective income tax rate differs from the U.S. statutory federal income tax rate primarily due to U.S. statutory depletion, state income taxes (net of federal tax benefit), nondeductible executive compensation over $1 million, foreign income, mining and withholding taxes, base erosion and anti-abuse tax, and valuation allowances recorded on deferred tax assets. The effective tax rates applied to the three months ended December 31, 2024 were determined by excluding the U.S. losses from the overall estimated annual effective tax rate computations and a separate estimated annual effective tax rate was computed and applied to the ordinary U.S. losses. Management assesses the available positive and negative evidence to estimate whether sufficient future taxable income will be generated to permit use of the existing deferred tax assets. A significant piece of objective negative evidence evaluated was the cumulative loss incurred in the U.S. over the three-year period ended December 31, 2024. Such objective evidence limits the ability to consider other subjective evidence, such as the Company’s projections for future income. On the basis of this evaluation, during the three months ended December 31, 2024, an additional valuation allowance of $9.5 million has been recorded to recognize only the portion of the U.S. deferred tax assets that is more likely than not to be realized. The amount of the deferred tax assets considered realizable, however, could be adjusted if objective negative evidence in the form of cumulative losses is no longer present and additional weight is given to subjective evidence such as the Company’s projections for income. As of December 31, 2024 and September 30, 2024, the Company had $78.4 million and $76.4 million, respectively of gross federal NOL carryforwards that have no expiration date and $6.6 million and $6.1 million at December 31, 2024 and September 30, 2024, respectively of net operating tax-effected state NOL carryforwards which expire beginning in 2031. Canadian provincial tax authorities have challenged tax positions claimed by one of the Company’s Canadian subsidiaries and have issued tax reassessments for fiscal years 2002-2019. The reassessments are a result of ongoing audits and total $192.8 million, including interest, through December 31, 2024. The Company disputes these reassessments and will continue to work with the appropriate authorities in Canada to resolve the dispute. There is a reasonable possibility that the ultimate resolution of this dispute, and any related disputes for other open tax years, may be materially higher or lower than the amounts the Company has reserved for such disputes. In connection with this dispute, local regulations require the Company to post security with the tax authority until the dispute is resolved. The Company has posted collateral in the form of a $152.3 million performance bond and has paid $34.6 million to the Canadian tax authorities (most of which is recorded in other assets in the Consolidated Balance Sheets at December 31, 2024, and September 30, 2024), which is necessary to proceed with future appeals or litigation. The Company expects that it will be required by local regulations to provide security for additional interest on the above unresolved disputed amounts and for any future reassessments issued by these Canadian tax authorities in the form of cash, letters of credit, performance bonds, asset liens or other arrangements agreeable with the tax authorities until the disputes are resolved. The Company expects that the ultimate outcome of these matters will not have a material impact on its results of operations or financial condition. However, the Company can provide no assurance as to the ultimate outcome of these matters, and the impact could be material if they are not resolved in the Company’s favor. As of December 31, 2024, the Company believes it has adequately reserved for these reassessments. Additionally, the Company has other uncertain tax positions as well as assessments and disputed positions with taxing authorities in its various jurisdictions, which are consistent with those matters disclosed in the Company’s 2024 Form 10-K.

Long-Term Debt

Long-Term Debt	3 Months Ended
	Dec. 31, 2024
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt: Long-term debt consists of the following (in millions): December 31, September 30, 6.75% Senior Notes due December 2027 $ 500.0 $ 500.0 Term Loan due May 2028 192.5 193.8 Revolving Credit Facility due May 2028 229.6 190.1 AR Securitization Facility expires March 2027 58.2 38.9 980.3 922.8 Less unamortized debt issuance costs (5.9) (5.3) Total debt 974.4 917.5 Less current portion (8.7) (7.5) Long-term debt $ 965.7 $ 910.0 On December 12, 2024, the Company entered into an amendment to its 2023 Credit Agreement, which, among other things, eased the restrictions of certain covenants contained in the agreement. The amendment included increasing the maximum allowed consolidated total net leverage ratio (as defined and calculated under the terms of the amended 2023 Credit Agreement) to 6.5x as of the last day of any quarter through the fiscal quarter ended September 30, 2025, then gradually stepping down to 4.50x for the fiscal quarter ended December 31, 2026 and thereafter. The amendment also decreased the Revolving Commitments (as defined in the Existing Credit Agreement) from $375 million to $325 million with additional reductions stepping down to $250 million on July 1, 2026. In connection with this amendment, the Company paid fees totaling $2.0 million which were capitalized as deferred financing costs. Additional arrangement and legal fees of $1.0 million were expensed as of December 31, 2024. As of December 31, 2024, the term loan and revolving credit facility under the 2023 Credit Agreement were secured by substantially all existing and future U.S. assets of the Company, the Goderich mine in Ontario, Canada and capital stock of certain subsidiaries. As of December 31, 2024 and September 30, 2024, the weighted average interest rate on all borrowings outstanding under the 2023 Credit Agreement was approximately 7.3% and 7.7%, respectively. Depending on the type, borrowings under the 2023 Credit Agreement accrue interest at a rate per annum equal to the Adjusted Term SOFR Rate, the Adjusted EURIBO Rate, Prime Rate or the CDO Rate (as defined in the credit agreement), as applicable, plus Applicable Margins (as defined in the credit agreement) which resulted in interest rates between 7.2% and 7.6% as of December 31, 2024, and 7.3% and 9.5% as of September 30, 2024. Outstanding letters of credit totaling $14.9 million as of December 31, 2024 further reduced available borrowing capacity under the Company’s $325 million revolving credit facility to $80.5 million. The 2023 Credit Agreement requires the Company to maintain certain financial ratios, including a minimum interest coverage ratio and a maximum total net leverage ratio. The Company was in compliance as of December 31, 2024 with its debt covenants under the 2023 Credit Agreement and its AR Securitization Facility. The consolidated total net leverage ratio represents the ratio of (a) consolidated total net debt to (b) consolidated adjusted earnings before interest, taxes, depreciation and amortization. Consolidated total net debt includes the aggregate principal amount of total debt, net of unrestricted cash not to exceed $75.0 million.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies: On October 21, 2022, a putative securities class was filed in the United States District Court for the District of Kansas. The lawsuit alleges that the Company and certain former executives of the Company made misleading statements and that shareholders were damaged by these statements. Plaintiffs filed an Amended Complaint on March 13, 2023; the Company filed a Motion to Dismiss on May 12, 2023. On December 12, 2023, the court granted and denied in part the Company’s Motion to Dismiss. On December 29, 2023, the Company filed a request for an interlocutory appeal and a request for a stay of discovery. On March 15, 2024, the Court denied the Company’s request for an interlocutory appeal. The parties participated in a mediation on November 19, 2024; the parties did not resolve the matter at mediation. On February 7, 2024, the parties reached an agreement in principle to resolve the matter and filed a motion to stay discovery. The agreement is preliminary and subject to final documentation, preliminary court approval and final approval after a court hearing. At this time, based on currently available information and its applicable insurance coverage, the Company believes any settlement to be paid will be covered by insurance and does not believe any losses will have a material adverse effect on its results of operations or cash flows in future periods. Additionally, the Company has recorded an estimated liability and estimated insurance recoveries in its Consolidated Balance Sheets as of December 31, 2024. On February 1, 2023, a shareholder derivative lawsuit was filed in the District of Kansas by an individual shareholder, purportedly on behalf of the Company. The lawsuit alleges that certain directors and executives breached their fiduciary duties to shareholders by failing to prevent the dissemination of misstatements and omissions from October 30, 2017, to November 18, 2018. The parties have stipulated to stay this matter through the discovery stage of the putative securities class action. On October 30, 2024, an additional shareholder derivative lawsuit was filed in the District of Kansas by an individual shareholder, purportedly on behalf of the Company. The lawsuit alleges that certain directors and executives breached their fiduciary duties to shareholders by willfully or recklessly causing the Company to make false and/or misleading statements and/or omissions of material fact from October 31, 2017, to October 21, 2022. The Company is also involved in legal and administrative proceedings and claims of various types from the ordinary course of the Company’s business. Management cannot predict the outcome of legal claims and proceedings with certainty. Nevertheless, management believes that the outcome of legal proceedings and claims, which are pending or known to be threatened, even if determined adversely, will not, individually or in the aggregate, have a material adverse effect on the Company’s results of operations, cash flows or financial position, except as otherwise described in Note 6 and this Note 8. The Company also has contingent consideration liabilities related to the Fortress North America, LLC (“Fortress”) acquisition. Refer to Note 12 for additional information. On October 25, 2024, the Company issued a recall for nine production lots of food-grade salt produced at its Goderich Plant following a customer report of a non-organic, foreign material in its product. The products recalled included both products sold prior and subsequent to September 30, 2024. The Company followed recall protocol and notified its BRCGS Global Standard for Food Safety certifying body, the Canadian Food Inspection Agency (“CFIA”) and the U.S. Food and Drug Administration (“FDA”). The Company has been working to obtain and assess the reported foreign material, complete the necessary investigation, and determine the next steps. For the three months ended December 31, 2024, the Company recognized $0.9 million for costs related to the recall on the Consolidated Statements of Operations, a portion of which the Company believes is reimbursable by insurance. Additionally, as of December 31, 2024, the Company has recorded a liability of $35.0 million and estimated insurance recoveries of $35.0 million in its Consolidated Balance Sheets associated with customer claims. The Company continues to assess the scope and magnitude of additional customer claims. At this time, based on currently available information and its applicable insurance coverage, the Company does not believe any incremental losses will have a material adverse effect on its results of operations or cash flows in future periods.

Operating Segments

Operating Segments	3 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Operating Segments	Operating Segments: The Company’s reportable segments are strategic business units that offer different products and services, and each business requires different technology and marketing strategies. For the three months ended December 31, 2024 and 2023, the Company has presented two reportable segments in its Consolidated Financial Statements: Salt and Plant Nutrition. The Salt segment produces and markets salt, consisting of sodium chloride and magnesium chloride, for use in road deicing for winter roadway safety and for dust control, food processing, water softening and other consumer, agricultural and industrial applications. The Plant Nutrition segment produces and markets various grades of SOP. The results of operations for the Company’s fire retardant and records management businesses are included in Corporate and Other in the tables below. Segment information is as follows (in millions): Three Months Ended December 31, 2024 Salt Plant Corporate & Other (a) Total Sales to external customers $ 242.2 $ 61.4 $ 3.6 $ 307.2 Intersegment sales — 3.2 (3.2) — Shipping and handling cost 71.3 9.3 — 80.6 Operating earnings (loss) (b) 29.4 (3.1) (25.8) 0.5 Depreciation, depletion and amortization 17.5 7.5 1.8 26.8 Total assets (as of end of period) 1,092.4 388.1 240.4 1,720.9 Three Months Ended December 31, 2023 Salt Plant Corporate & Other (a) Total Sales to external customers $ 274.3 $ 49.7 $ 17.7 $ 341.7 Intersegment sales — 3.1 (3.1) — Shipping and handling cost 83.7 7.0 0.6 91.3 Operating earnings (loss) (b)(c) 50.9 (2.3) (102.2) (53.6) Depreciation, depletion and amortization 15.2 8.4 1.9 25.5 Total assets (as of end of period) 1,056.6 469.7 278.9 1,805.2 Disaggregated revenue by product type is as follows (in millions): Three Months Ended December 31, 2024 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 138.1 $ — $ — $ 138.1 Consumer & Industrial Salt 104.1 — — 104.1 SOP — 64.6 — 64.6 Eliminations & Other — (3.2) 3.6 0.4 Sales to external customers $ 242.2 $ 61.4 $ 3.6 $ 307.2 Three Months Ended December 31, 2023 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 159.4 $ — $ — $ 159.4 Consumer & Industrial Salt 114.9 — — 114.9 SOP — 52.8 — 52.8 Fire Retardant — — 14.0 14.0 Revenue from Services — — 0.5 0.5 Eliminations & Other — (3.1) 3.2 0.1 Sales to external customers $ 274.3 $ 49.7 $ 17.7 $ 341.7 (a) Corporate and Other includes corporate entities, records management operations, the Fortress fire retardant business, equity method investments, prior-year lithium costs and other incidental operations and eliminations. Operating earnings (loss) for corporate and other includes indirect corporate overhead, including costs for general corporate governance and oversight, prior-year lithium-related expenses, as well as costs for the human resources, information technology, legal and finance functions. (b) Corporate operating results were impacted by costs related to a product recall of $0.9 million for the three months ended December 31, 2024. Corporate operating results were also impacted by a net loss of $1.6 million related to an increase in the valuation of the Fortress contingent consideration for the three months ended Dec. 31, 2023. (c) As a result of the Company’s decision to cease the pursuit of the lithium development, the Company recognized an impairment of long-lived assets of $74.8 million for the three months ended December 31, 2023. The Company also recognized severance of $2.5 million related to the termination of the lithium development and $1.1 million related to other restructuring, which impacted operating results for the three months ended December 31, 2023. The Company’s revenue by geographic area is as follows (in millions): Three Months Ended Revenue 2024 2023 United States (a) $ 212.7 $ 250.9 Canada 79.3 77.6 United Kingdom 11.2 13.0 Other 4.0 0.2 Total revenue $ 307.2 $ 341.7 (a) United States sales exclude product sold to foreign customers at U.S. ports.

Stockholders' Equity and Equity

Stockholders' Equity and Equity Instruments	3 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Stockholders' Equity and Equity Instruments	Stockholders’ Equity and Equity Instruments: Equity Compensation Awards In May 2020, the Company’s stockholders approved the 2020 Incentive Award Plan (as amended, the “2020 Plan”), which authorized the issuance of 2,977,933 shares of Company common stock. In February 2022, the Company’s stockholders approved an amendment to the 2020 Plan authorizing an additional 750,000 shares of Company stock. In March 2024, the Company’s stockholders approved an amendment to the 2020 Plan authorizing an additional 3,000,000 shares of Company stock. Since the date the 2020 Plan was approved, the Company ceased issuing equity awards under the 2015 Incentive Award Plan (as amended, the “2015 Plan”). Since the approval of the 2015 Plan in May 2015, the Company ceased issuing equity awards under the 2005 Incentive Award Plan (as amended, the “2005 Plan”). The 2005 Plan, the 2015 Plan and the 2020 Plan allow for grants of equity awards to executive officers, other employees and directors, including restricted stock units (“RSUs”), performance stock units (“PSUs”), stock options and deferred stock units. For additional information regarding equity awards issued under the Company’s incentive plans refer to “Note 15 – Stockholder’s Equity and Equity Instruments” within Part II, Item 8 of its 2024 Form 10-K. During the three months ended December 31, 2024, the Company reissued the following number of shares from treasury stock: 108,023 shares related to the release of RSUs which vested and 10,224 shares issued for Board of Director compensation. In fiscal 2024, the Company issued 222,155 net shares from treasury stock. The Company withheld a total of 34,955 shares with a fair value of $0.5 million related to the vesting of RSUs during the three months ended December 31, 2024. The fair value of the shares was valued at the closing price at the vesting date and represent the employee tax withholding for the employee’s compensation. The Company recognized tax expense of $0.5 million from its equity compensation awards during the three months ended December 31, 2024. During the three months ended December 31, 2024 and 2023, the Company recorded $3.9 million and $11.9 million, respectively, of compensation expense pursuant to its stock-based compensation plans. No amounts have been capitalized. PSUs During the three months ended December 31, 2024, the Company issued new PSUs based upon performance criteria and metrics (“Scorecard PSUs”). The actual number of shares of common stock that may be earned with respect to Scorecard PSUs is calculated based upon the attainment of certain thresholds for free cash flow and return on capital employed during each year of the three-year performance period and may range from 0% to 200% for each measure. Additionally, a modifier will increase or decrease the payout by 20% based upon relative total shareholder return against the Company’s peer group. The following table summarizes stock-based compensation activity during the three months ended December 31, 2024: Stock Options RSUs PSUs (a) Number Weighted-average Number Weighted-average Number Weighted-average Outstanding at September 30, 2024 187,023 $ 62.85 451,091 $ 27.93 229,469 $ 40.26 Granted — — 749,627 12.83 214,673 16.57 Exercised (b) — — — — — — Released from restriction (b) — — (108,023) 32.70 — — Cancelled/expired (3,279) 64.12 (5,843) 18.03 — — Outstanding at December 31, 2024 183,744 $ 62.83 1,086,852 $ 17.09 444,142 $ 28.81 (a) Until the performance period is completed, PSUs are included in the table at the target level at their grant date and at that level represent one share of common stock per PSU. (b) Common stock issued for exercised options and for vested and earned RSUs and PSUs was issued from treasury stock. Accumulated Other Comprehensive Loss (“AOCL”) The Company’s comprehensive income (loss) is comprised of net loss, net amortization of the unrealized loss of the pension obligation, the change in the unrealized gain in other postretirement benefits, the change in the unrealized gain (loss) on natural gas and foreign currency cash flow hedges and currency translation adjustment (“CTA”). The components of and changes in AOCL are as follows (in millions): Three Months Ended December 31, 2024 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (1.3) $ (6.2) $ 1.4 $ (90.3) $ (96.4) Other comprehensive loss before reclassifications (b) (0.9) — — (33.3) (34.2) Amounts reclassified from AOCL 0.6 0.2 (0.1) — 0.7 Net current period other comprehensive income (loss) (0.3) 0.2 (0.1) (33.3) (33.5) Ending balance $ (1.6) $ (6.0) $ 1.3 $ (123.6) $ (129.9) Three Months Ended December 31, 2023 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (1.4) $ (6.6) $ 1.7 $ (98.4) $ (104.7) Other comprehensive income before reclassifications (b) (2.6) — — 14.6 12.0 Amounts reclassified from AOCL 0.8 0.2 — — 1.0 Net current period other comprehensive income (1.8) 0.2 — 14.6 13.0 Ending balance $ (3.2) $ (6.4) $ 1.7 $ (83.8) $ (91.7) (a) With the exception of the CTA, for which no tax effect is recorded, the changes in the components of AOCL presented in the tables above are reflected net of applicable income taxes. (b) The Company recorded foreign exchange gain (loss) of $5.4 million and $(2.3) million in the three months ended December 31, 2024 and 2023, respectively, in AOCL related to intercompany notes which were deemed to be of a long-term investment nature. The amounts reclassified from AOCL to expense (income) for the three months ended December 31, 2024 and 2023, are shown below (in millions): Amount Reclassified from AOCL Three Months Ended Line Item Impacted in the 2024 2023 Loss (gain) on cash flow hedges: Natural gas instruments $ 0.6 $ 0.8 Product cost Income tax expense — — Reclassifications, net of income taxes 0.6 0.8 Amortization of defined benefit pension: Amortization of loss 0.3 0.3 Product cost Income tax benefit (0.1) (0.1) Reclassifications, net of income taxes 0.2 0.2 Amortization of other post-employment benefits: Amortization of gain (0.1) — Product cost Income tax expense — — Reclassifications, net of income taxes (0.1) — Total reclassifications, net of income taxes $ 0.7 $ 1.0

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments: The Company is subject to various types of market risks, including interest rate risk, foreign currency exchange rate transaction and translation risk and commodity pricing risk. Management may take actions to mitigate the exposure to these types of risks, including entering into forward purchase contracts and other financial instruments. The Company manages a portion of its commodity pricing risks and foreign currency exchange rate risks by using derivative instruments. From time to time, the Company may enter into foreign exchange contracts to mitigate foreign exchange risk. The Company does not seek to engage in trading activities or take speculative positions with any financial instrument arrangement. The Company enters into natural gas derivative instruments and foreign currency derivative instruments with counterparties it views as creditworthy. However, the Company does attempt to mitigate its counterparty credit risk exposures by, among other things, entering into master netting agreements with some of these counterparties. The Company records derivative financial instruments as either assets or liabilities at fair value in its Consolidated Balance Sheets. The assets and liabilities recorded as of December 31, 2024 and September 30, 2024 were not material. Derivatives qualify for treatment as hedges when there is a high correlation between the change in fair value of the derivative instrument and the related change in value of the underlying hedged item. Depending on the exposure being hedged, the Company must designate the hedging instrument as a fair value hedge, a cash flow hedge or a net investment in foreign operations hedge. For the qualifying derivative instruments that have been designated as cash flow hedges, the effective portion of the change in fair value is recognized through earnings when the underlying transaction being hedged affects earnings, allowing a derivative’s gains and losses to offset related results from the hedged item in the Consolidated Statements of Operations. Any ineffectiveness related to these instruments accounted for as hedges was not material for any of the periods presented. For derivative instruments that have not been designated as hedges, the entire change in fair value is recorded through earnings in the period of change. Natural Gas Derivative Instruments Natural gas is consumed at several of the Company’s production facilities, and changes in natural gas prices impact the Company’s operating margin. The Company seeks to reduce the earnings and cash flow impacts of changes in market prices of natural gas by fixing the purchase price of up to 90% of its forecasted natural gas usage. It is the Company’s policy to consider hedging portions of its natural gas usage up to 36 months in advance of the forecasted purchase. As of December 31, 2024, the Company had entered into natural gas derivative instruments to hedge a portion of its natural gas purchase requirements through September 2026. As of December 31, 2024 and September 30, 2024, the Company had agreements in place to hedge forecasted natural gas purchases of 2.6 million a nd 2.3 million MMBtus, respectively. All natural gas derivative instruments held by the Company as of December 31, 2024 and September 30, 2024 qualified and were designated as cash flow hedges. As of December 31, 2024, the Company expects to reclassify from AOCL to earnings during the next twelve months $1.7 million of net losses on derivative instruments related to its natural gas hedges. Refer to Note 12 for the estimated fair value of the Company’s natural gas derivative instruments as of December 31, 2024 and September 30, 2024. The following tables present the fair value of the Company’s derivatives (in millions): Asset Derivatives Liability Derivatives Consolidated Balance Sheet Location December 31, 2024 Consolidated Balance Sheet Location December 31, 2024 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.3 Accrued expenses and other current liabilities $ 2.0 Commodity contracts Other assets 0.3 Other noncurrent liabilities 0.2 Total derivatives (a) $ 0.6 $ 2.2 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $0.6 million of its commodity contracts that are in receivable positions against its contracts in payable positions. Asset Derivatives Liability Derivatives Consolidated Balance Sheet Location September 30, 2024 Consolidated Balance Sheet Location September 30, 2024 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.5 Accrued expenses and other current liabilities $ 1.7 Commodity contracts Other assets 0.1 Other noncurrent liabilities 0.2 Total derivatives (a) $ 0.6 $ 1.9 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $0.6 million of its commodity contracts that are in receivable positions against its contracts in payable positions.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Dec. 31, 2024
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), except as stated below. The Company holds marketable securities associated with its defined 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 ). 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. The estimated fair values for each type of instrument are presented below (in millions): December 31, Level One Level Two Level Three Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 3.4 $ 3.4 $ — $ — Derivatives – natural gas instruments, net 0.6 — 0.6 — Total Assets $ 4.0 $ 3.4 $ 0.6 $ — Liability Class: Derivatives - natural gas instruments, net $ (2.2) $ — $ (2.2) $ — Liabilities related to non-qualified savings plan (3.4) (3.4) — — Total Liabilities $ (5.6) $ (3.4) $ (2.2) $ — (a) Includes mutual fund investments of approximately 25% in common stock of large-cap U.S. companies, 5% in common stock of small to mid-cap U.S. companies, 10% in bond funds, 20% in short-term investments and 40% in blended funds. September 30, Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 3.1 $ 3.1 $ — $ — Derivatives - natural gas instruments, net 0.6 — 0.6 — Total Assets $ 3.7 $ 3.1 $ 0.6 $ — Liability Class: Derivatives - natural gas instruments, net $ (1.9) $ — $ (1.9) $ — Liabilities related to non-qualified savings plan (3.1) (3.1) — — Total Liabilities $ (5.0) $ (3.1) $ (1.9) $ — (a) Includes mutual fund investments of approximately 35% in the common stock of large-cap U.S. companies, 5% in the common stock of small to mid-cap U.S. companies, 5% in the common stock of international companies, 10% in bond funds, 5% in short-term investments and 40% in blended funds. 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. The Company’s investments related to its non-qualified retirement plan of $3.4 million at December 31, 2024 and $3.1 million at September 30, 2024, are stated at fair value based on quoted market prices. As of December 31, 2024 and September 30, 2024, the estimated fair value of the Company’s fixed-rate 6.75% Senior Notes due December 2027, based on available trading information (Level 2), totaled $492.5 million and $497.0 million, respectively, compared with the aggregate principal amount at maturity of $500.0 million. The fair value at December 31, 2024 and September 30, 2024 of amounts outstanding under the Company’s term loans and revolving credit facility, based upon available bid information received from the Company’s lender (Level 2), totaled approximately $416.8 million and $379.1 million, respectively, compared with the aggregate principal amount at maturity of $422.1 million and $383.9 million, respectively. In connection with the acquisition of Fortress on May 5, 2023, the Company entered into a contingent consideration arrangement for up to $28 million to be paid in cash and/or Compass Minerals common stock upon the achievement of certain performance measures over the next five years, and a cash earn-out based on volumes of certain Fortress fire retardant products sold over a 10-year period. The fair value of the milestone contingent consideration is estimated using a probability-weighted discounted cash flow model with significant inputs not observable in the market and is therefore considered a Level 3 measurement while the earn-out is valued using a Monte Carlo simulation, also a Level 3 measurement. For the three months ended December 31, 2024, the total fair value of the contingent consideration did not change. For the three months ended December 31, 2023, the Company recorded an expense of $1.6 million. The change in the three months ended December 31, 2023 was reflective of updated financial performance, changes in discount rates and the passage of time. The change is recorded in other operating (income) expense in the Consolidated Statements of Operations to reflect the contingent consideration liability at its fair value as of December 31, 2023. The Company will continue to recognize remeasurement changes in the estimated fair value of contingent consideration in earnings at each reporting date until all contingencies are resolved. The following table presents the fair value of the Company’s total contingent consideration arrangement (in millions): Consolidated Balance Sheet Location December 31, 2024 September 30, 2024 Accrued expenses and other current liabilities $ 0.1 $ — Other noncurrent liabilities 7.8 7.9 Total contingent consideration $ 7.9 $ 7.9 The Company has certain assets, including goodwill and other intangible assets, which are measured at fair value on a non-recurring basis and are adjusted to fair value only if an impairment charge is recognized. The categorization of the framework used to measure fair value of the assets is considered to be within the Level 3 valuation hierarchy due to the subjective nature of the unobservable inputs used. Refer to Note 5

Earnings per Share

Earnings per Share	3 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share: On April 22, 2024, the Board of Directors determined not to declare dividends for the foreseeable future in order to align the Company’s capital allocation priorities with its corporate focus on accelerating cash flow generation and debt reduction. The Company calculated earnings per share using the treasury stock method during the three months ended December 31, 2024. The following table sets forth the computation of basic and diluted earnings per common share (in millions, except for share and per-share data): Three Months Ended 2024 2023 Numerator: Net loss $ (23.6) $ (75.3) Less: net earnings allocated to participating securities (a) — (0.1) Net loss available to common stockholders $ (23.6) $ (75.4) Denominator (in thousands): Weighted-average common shares outstanding, shares for basic earnings per share (b) 41,441 41,205 Weighted-average awards outstanding — — Shares for diluted earnings per share 41,441 41,205 Basic net loss per common share $ (0.57) $ (1.83) Diluted net loss per common share $ (0.57) $ (1.83) (a) Weighted participating securities include RSUs and PSUs that receive non-forfeitable dividends and consist of 1,116,000 weighted participating securities for the three months ended December 31, 2024 and 777,000 weighted participating securities for the three months ended December 31, 2023. (b)

Related Party Transactions

Related Party Transactions	3 Months Ended
	Dec. 31, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions:During both the three months ended December 31, 2024 and 2023, the Company recorded SOP sales of approximately $1.1 million and $0.8 million, respectively, to certain subsidiaries of Koch Industries, Inc. As of December 31, 2024 and September 30, 2024, the Company had approximately $0.6 million and $0.3 million, respectively, of receivables from related parties on its Consolidated Balance Sheets. There were no amounts payable outstanding as of December 31, 2024.

Subsequent Events

Subsequent Events	3 Months Ended
	Dec. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events: [ ]

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (23.6)	$ (75.3)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Accounting Policies and Basis_2

Accounting Policies and Basis of Presentation (Policies)	3 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Basis of Consolidation	CMI is a holding company with no significant operations other than those of its wholly-owned subsidiaries. The consolidated financial statements include the accounts of CMI and its wholly-owned domestic and foreign subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Basis of Presentation	The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete consolidated financial statements. These unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements of the Company for the annual period ended September 30, 2024, as filed with the Securities and Exchange Commission (the “SEC”) in its Annual Report on Form 10-K on December 16, 2024 (“2024 Form 10-K”). In the opinion of management, all adjustments, consisting of normal recurring adjustments considered necessary for a fair presentation, have been included.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-07, “Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures”, which updates reportable segment disclosure requirements primarily to include enhanced disclosures about significant segment expenses. The amendments are effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied retrospectively to all prior periods presented in the financial statements. Management is currently evaluating this ASU to determine its impact on the Company's disclosures. In December 2023, the FASB issued ASU 2023-09, “Income Taxes (Topic 740): Improvements to Income Tax Disclosures”, which updates income tax disclosures by requiring consistent categories and additional disaggregation of information in the rate reconciliation and income taxes paid by jurisdiction. The amendments are effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. The amendments should be applied prospectively; however, retrospective application is permitted. Management is currently evaluating this ASU to determine its impact on the Company’s disclosures. In November 2024, the FASB issued amended guidance related to disclosure of disaggregated expenses (“ASU 2024-03”). This amendment requires public business entities to provide detailed disclosures in the notes to financial statements disaggregating specific expense categories, including employee compensation, depreciation, and intangible asset amortization, as well as certain other disclosures to provide enhanced transparency into the nature and function of expenses. This new guidance is effective for annual periods beginning in the Company’s fiscal 2028 and interim periods following annual adoption, with early adoption permitted. This guidance will be applied on a prospective basis with retrospective application permitted. Management is currently evaluating this ASU to determine its impact on the Company’s disclosures.
Deferred Revenue	Deferred Revenue
Derivative Financial Instruments	The Company is subject to various types of market risks, including interest rate risk, foreign currency exchange rate transaction and translation risk and commodity pricing risk. Management may take actions to mitigate the exposure to these types of risks, including entering into forward purchase contracts and other financial instruments. The Company manages a portion of its commodity pricing risks and foreign currency exchange rate risks by using derivative instruments. From time to time, the Company may enter into foreign exchange contracts to mitigate foreign exchange risk. The Company does not seek to engage in trading activities or take speculative positions with any financial instrument arrangement. The Company enters into natural gas derivative instruments and foreign currency derivative instruments with counterparties it views as creditworthy. However, the Company does attempt to mitigate its counterparty credit risk exposures by, among other things, entering into master netting agreements with some of these counterparties. The Company records derivative financial instruments as either assets or liabilities at fair value in its Consolidated Balance Sheets. The assets and liabilities recorded as of December 31, 2024 and September 30, 2024 were not material.

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Dec. 31, 2024
Inventory Disclosure [Abstract]
Schedule of Inventories	Inventories consist of the following (in millions): December 31, September 30, Finished goods $ 286.8 $ 336.5 Work in process 6.4 6.4 Raw materials and supplies (a) 73.9 71.2 Total inventories $ 367.1 $ 414.1 (a)

Property, Plant and Equipment_2

Property, Plant and Equipment, Net (Tables)	3 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment, Net	Property, plant and equipment, net, consists of the following (in millions): December 31, September 30, Land, buildings and structures, and leasehold improvements $ 550.2 $ 559.8 Machinery and equipment 1,120.2 1,149.5 Office furniture and equipment 23.9 24.1 Mineral interests 166.5 170.4 Construction in progress 57.5 56.0 1,918.3 1,959.8 Less: accumulated depreciation and depletion (1,139.7) (1,153.3) Property, plant and equipment, net $ 778.6 $ 806.5

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in the Carrying Amount of Goodwill	Changes in the carrying amount of goodwill are summarized as follows (in millions): Corporate & Other Balance as of September 30, 2024 $ 6.0 Foreign currency translation adjustment (0.2) Balance as of December 31, 2024 $ 5.8

Long-Term Debt (Tables)

Long-Term Debt (Tables)	3 Months Ended
	Dec. 31, 2024
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-term debt consists of the following (in millions): December 31, September 30, 6.75% Senior Notes due December 2027 $ 500.0 $ 500.0 Term Loan due May 2028 192.5 193.8 Revolving Credit Facility due May 2028 229.6 190.1 AR Securitization Facility expires March 2027 58.2 38.9 980.3 922.8 Less unamortized debt issuance costs (5.9) (5.3) Total debt 974.4 917.5 Less current portion (8.7) (7.5) Long-term debt $ 965.7 $ 910.0

Operating Segments (Tables)

Operating Segments (Tables)	3 Months Ended
	Dec. 31, 2024
Segment Reporting [Abstract]
Schedule of Segment Information	Segment information is as follows (in millions): Three Months Ended December 31, 2024 Salt Plant Corporate & Other (a) Total Sales to external customers $ 242.2 $ 61.4 $ 3.6 $ 307.2 Intersegment sales — 3.2 (3.2) — Shipping and handling cost 71.3 9.3 — 80.6 Operating earnings (loss) (b) 29.4 (3.1) (25.8) 0.5 Depreciation, depletion and amortization 17.5 7.5 1.8 26.8 Total assets (as of end of period) 1,092.4 388.1 240.4 1,720.9 Three Months Ended December 31, 2023 Salt Plant Corporate & Other (a) Total Sales to external customers $ 274.3 $ 49.7 $ 17.7 $ 341.7 Intersegment sales — 3.1 (3.1) — Shipping and handling cost 83.7 7.0 0.6 91.3 Operating earnings (loss) (b)(c) 50.9 (2.3) (102.2) (53.6) Depreciation, depletion and amortization 15.2 8.4 1.9 25.5 Total assets (as of end of period) 1,056.6 469.7 278.9 1,805.2
Schedule of Disaggregated Revenue by Product Type	Disaggregated revenue by product type is as follows (in millions): Three Months Ended December 31, 2024 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 138.1 $ — $ — $ 138.1 Consumer & Industrial Salt 104.1 — — 104.1 SOP — 64.6 — 64.6 Eliminations & Other — (3.2) 3.6 0.4 Sales to external customers $ 242.2 $ 61.4 $ 3.6 $ 307.2 Three Months Ended December 31, 2023 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 159.4 $ — $ — $ 159.4 Consumer & Industrial Salt 114.9 — — 114.9 SOP — 52.8 — 52.8 Fire Retardant — — 14.0 14.0 Revenue from Services — — 0.5 0.5 Eliminations & Other — (3.1) 3.2 0.1 Sales to external customers $ 274.3 $ 49.7 $ 17.7 $ 341.7 (a) Corporate and Other includes corporate entities, records management operations, the Fortress fire retardant business, equity method investments, prior-year lithium costs and other incidental operations and eliminations. Operating earnings (loss) for corporate and other includes indirect corporate overhead, including costs for general corporate governance and oversight, prior-year lithium-related expenses, as well as costs for the human resources, information technology, legal and finance functions. (b) Corporate operating results were impacted by costs related to a product recall of $0.9 million for the three months ended December 31, 2024. Corporate operating results were also impacted by a net loss of $1.6 million related to an increase in the valuation of the Fortress contingent consideration for the three months ended Dec. 31, 2023. (c)
Schedule of Revenue by Geographic Area	The Company’s revenue by geographic area is as follows (in millions): Three Months Ended Revenue 2024 2023 United States (a) $ 212.7 $ 250.9 Canada 79.3 77.6 United Kingdom 11.2 13.0 Other 4.0 0.2 Total revenue $ 307.2 $ 341.7 (a) United States sales exclude product sold to foreign customers at U.S. ports.

Stockholders' Equity and Equi_2

Stockholders' Equity and Equity Instruments (Tables)	3 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Schedule of Stock-Based Compensation Activity	The following table summarizes stock-based compensation activity during the three months ended December 31, 2024: Stock Options RSUs PSUs (a) Number Weighted-average Number Weighted-average Number Weighted-average Outstanding at September 30, 2024 187,023 $ 62.85 451,091 $ 27.93 229,469 $ 40.26 Granted — — 749,627 12.83 214,673 16.57 Exercised (b) — — — — — — Released from restriction (b) — — (108,023) 32.70 — — Cancelled/expired (3,279) 64.12 (5,843) 18.03 — — Outstanding at December 31, 2024 183,744 $ 62.83 1,086,852 $ 17.09 444,142 $ 28.81 (a) Until the performance period is completed, PSUs are included in the table at the target level at their grant date and at that level represent one share of common stock per PSU. (b) Common stock issued for exercised options and for vested and earned RSUs and PSUs was issued from treasury stock.
Schedule of Components and Changes in Accumulated Other Comprehensive Income (Loss)	The components of and changes in AOCL are as follows (in millions): Three Months Ended December 31, 2024 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (1.3) $ (6.2) $ 1.4 $ (90.3) $ (96.4) Other comprehensive loss before reclassifications (b) (0.9) — — (33.3) (34.2) Amounts reclassified from AOCL 0.6 0.2 (0.1) — 0.7 Net current period other comprehensive income (loss) (0.3) 0.2 (0.1) (33.3) (33.5) Ending balance $ (1.6) $ (6.0) $ 1.3 $ (123.6) $ (129.9) Three Months Ended December 31, 2023 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (1.4) $ (6.6) $ 1.7 $ (98.4) $ (104.7) Other comprehensive income before reclassifications (b) (2.6) — — 14.6 12.0 Amounts reclassified from AOCL 0.8 0.2 — — 1.0 Net current period other comprehensive income (1.8) 0.2 — 14.6 13.0 Ending balance $ (3.2) $ (6.4) $ 1.7 $ (83.8) $ (91.7) (a) With the exception of the CTA, for which no tax effect is recorded, the changes in the components of AOCL presented in the tables above are reflected net of applicable income taxes. (b) The Company recorded foreign exchange gain (loss) of $5.4 million and $(2.3) million in the three months ended December 31, 2024 and 2023, respectively, in AOCL related to intercompany notes which were deemed to be of a long-term investment nature.
Schedule of Amounts Reclassified from AOCL to Expense (Income)	The amounts reclassified from AOCL to expense (income) for the three months ended December 31, 2024 and 2023, are shown below (in millions): Amount Reclassified from AOCL Three Months Ended Line Item Impacted in the 2024 2023 Loss (gain) on cash flow hedges: Natural gas instruments $ 0.6 $ 0.8 Product cost Income tax expense — — Reclassifications, net of income taxes 0.6 0.8 Amortization of defined benefit pension: Amortization of loss 0.3 0.3 Product cost Income tax benefit (0.1) (0.1) Reclassifications, net of income taxes 0.2 0.2 Amortization of other post-employment benefits: Amortization of gain (0.1) — Product cost Income tax expense — — Reclassifications, net of income taxes (0.1) — Total reclassifications, net of income taxes $ 0.7 $ 1.0

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Fair Value of Derivatives	The following tables present the fair value of the Company’s derivatives (in millions): Asset Derivatives Liability Derivatives Consolidated Balance Sheet Location December 31, 2024 Consolidated Balance Sheet Location December 31, 2024 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.3 Accrued expenses and other current liabilities $ 2.0 Commodity contracts Other assets 0.3 Other noncurrent liabilities 0.2 Total derivatives (a) $ 0.6 $ 2.2 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $0.6 million of its commodity contracts that are in receivable positions against its contracts in payable positions. Asset Derivatives Liability Derivatives Consolidated Balance Sheet Location September 30, 2024 Consolidated Balance Sheet Location September 30, 2024 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.5 Accrued expenses and other current liabilities $ 1.7 Commodity contracts Other assets 0.1 Other noncurrent liabilities 0.2 Total derivatives (a) $ 0.6 $ 1.9 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $0.6 million of its commodity contracts that are in receivable positions against its contracts in payable positions.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Estimated Fair Values for Type of Instrument	The estimated fair values for each type of instrument are presented below (in millions): December 31, Level One Level Two Level Three Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 3.4 $ 3.4 $ — $ — Derivatives – natural gas instruments, net 0.6 — 0.6 — Total Assets $ 4.0 $ 3.4 $ 0.6 $ — Liability Class: Derivatives - natural gas instruments, net $ (2.2) $ — $ (2.2) $ — Liabilities related to non-qualified savings plan (3.4) (3.4) — — Total Liabilities $ (5.6) $ (3.4) $ (2.2) $ — (a) Includes mutual fund investments of approximately 25% in common stock of large-cap U.S. companies, 5% in common stock of small to mid-cap U.S. companies, 10% in bond funds, 20% in short-term investments and 40% in blended funds. September 30, Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 3.1 $ 3.1 $ — $ — Derivatives - natural gas instruments, net 0.6 — 0.6 — Total Assets $ 3.7 $ 3.1 $ 0.6 $ — Liability Class: Derivatives - natural gas instruments, net $ (1.9) $ — $ (1.9) $ — Liabilities related to non-qualified savings plan (3.1) (3.1) — — Total Liabilities $ (5.0) $ (3.1) $ (1.9) $ — (a) Includes mutual fund investments of approximately 35% in the common stock of large-cap U.S. companies, 5% in the common stock of small to mid-cap U.S. companies, 5% in the common stock of international companies, 10% in bond funds, 5% in short-term investments and 40% in blended funds.
Schedule of Total Contingent Consideration	The following table presents the fair value of the Company’s total contingent consideration arrangement (in millions): Consolidated Balance Sheet Location December 31, 2024 September 30, 2024 Accrued expenses and other current liabilities $ 0.1 $ — Other noncurrent liabilities 7.8 7.9 Total contingent consideration $ 7.9 $ 7.9

Earnings per Share (Tables)

Earnings per Share (Tables)	3 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Earnings Per Common Share	The following table sets forth the computation of basic and diluted earnings per common share (in millions, except for share and per-share data): Three Months Ended 2024 2023 Numerator: Net loss $ (23.6) $ (75.3) Less: net earnings allocated to participating securities (a) — (0.1) Net loss available to common stockholders $ (23.6) $ (75.4) Denominator (in thousands): Weighted-average common shares outstanding, shares for basic earnings per share (b) 41,441 41,205 Weighted-average awards outstanding — — Shares for diluted earnings per share 41,441 41,205 Basic net loss per common share $ (0.57) $ (1.83) Diluted net loss per common share $ (0.57) $ (1.83) (a) Weighted participating securities include RSUs and PSUs that receive non-forfeitable dividends and consist of 1,116,000 weighted participating securities for the three months ended December 31, 2024 and 777,000 weighted participating securities for the three months ended December 31, 2023. (b)

Revenues (Details)

Revenues (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Revenue from Contract with Customer [Abstract]
Deferred revenue	$ 3.6	$ 3.6

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Inventory Disclosure [Abstract]
Finished goods	$ 286.8	$ 336.5
Work in process	6.4	6.4
Raw materials and supplies	73.9	71.2
Total inventories	367.1	414.1
Raw materials and supplies, noncurrent	$ 41.1	$ 42.2

Property, Plant and Equipment_3

Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,918.3	$ 1,959.8
Less: accumulated depreciation and depletion	(1,139.7)	(1,153.3)
Property, plant and equipment, net	778.6	806.5
Land, buildings and structures, and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	550.2	559.8
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,120.2	1,149.5
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	23.9	24.1
Mineral interests
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	166.5	170.4
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 57.5	$ 56

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets (Details) $ in Millions	3 Months Ended
	Dec. 31, 2024 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 6
Goodwill, ending balance	5.8
Corporate and Other
Goodwill [Roll Forward]
Goodwill, beginning balance	6
Foreign currency translation adjustment	(0.2)
Goodwill, ending balance	$ 5.8

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Sep. 30, 2024
Income Tax Disclosure [Line Items]
Nondeductible executive compensation	$ 1
Prepaid taxes	11.2	$ 11
U.S. Federal
Income Tax Disclosure [Line Items]
Deferred tax asset valuation allowance recorded	9.5
Foreign Tax Authority
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	78.4	76.4
Foreign Tax Authority | Canadian Tax Authority
Income Tax Disclosure [Line Items]
Total reassessments including interest	192.8
Amount of security posted in the form of a performance bond	152.3
Amount of security posted in the form of cash	34.6	34.6
State and Local | NOL Carryforwards Expire Beginning in 2035
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 6.6	$ 6.1

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Debt Instrument [Line Items]
Long-term debt, gross	$ 980.3	$ 922.8
Less unamortized debt issuance costs	(5.9)	(5.3)
Total debt	974.4	917.5
Less current portion	(8.7)	(7.5)
Long-term debt	$ 965.7	$ 910
Senior Notes | 6.75% Senior Notes due December 2027
Debt Instrument [Line Items]
Stated interest rate	6.75%	6.75%
Long-term debt, gross	$ 500	$ 500
Line of Credit | Term Loan due May 2028
Debt Instrument [Line Items]
Long-term debt, gross	192.5	193.8
Line of Credit | Revolving Credit Facility due May 2028
Debt Instrument [Line Items]
Long-term debt, gross	229.6	190.1
Line of Credit | AR Securitization Facility expires March 2027
Debt Instrument [Line Items]
Long-term debt, gross	$ 58.2	$ 38.9

Long-Term Debt - Narrative (Det

Long-Term Debt - Narrative (Details) - Line of Credit	3 Months Ended
	Dec. 31, 2024 USD ($)	Jul. 01, 2026 USD ($)	Dec. 12, 2024 USD ($)	Sep. 30, 2024	Nov. 26, 2019 USD ($)
2023 Credit Agreement
Debt Instrument [Line Items]
Deferred financing costs	$ 2,000,000
Additional legal fees	1,000,000
2023 Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate principal amount of credit facility	325,000,000
Outstanding letters of credit	14,900,000
Availability under revolving credit facility	$ 80,500,000
2023 Credit Agreement | Fiscal Quarter Ended December 31, 2024
Debt Instrument [Line Items]
Consolidated total net leverage ratio			6.5
2023 Credit Agreement | Fiscal Quarter Ended March 31, 2026 and Thereafter
Debt Instrument [Line Items]
Consolidated total net leverage ratio			4.50
Revolving Credit Facility Due January 2025
Debt Instrument [Line Items]
Weighted average interest rate of debt (as a percent)	7.30%			7.70%
Revolving Credit Facility Due January 2025 | Minimum
Debt Instrument [Line Items]
Weighted average interest rate of debt (as a percent)	7.20%			7.30%
Revolving Credit Facility Due January 2025 | Maximum
Debt Instrument [Line Items]
Weighted average interest rate of debt (as a percent)	7.60%			9.50%
Revolving Credit Facility Due January 2025 | Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate principal amount of credit facility			$ 325,000,000		$ 375,000,000
Maximum unrestricted cash	$ 75,000,000
Revolving Credit Facility Due January 2025 | Revolving Credit Facility | Forecast
Debt Instrument [Line Items]
Aggregate principal amount of credit facility		$ 250,000,000

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	3 Months Ended
	Dec. 31, 2024 USD ($)	Oct. 25, 2024 productionLot
Commitments and Contingencies Disclosure [Abstract]
Number of production lots recalled | productionLot		9
Production recall expense	$ 0.9
Loss contingency, receivable	35
Estimated insurance recoveries	$ (35)

Operating Segments - Narrative

Operating Segments - Narrative (Details) - segment	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting [Abstract]
Number of reportable segments	2	2

Operating Segments - Schedule o

Operating Segments - Schedule of Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Sales	$ 307.2	$ 341.7
Operating earnings (loss)	0.5	(53.6)
Depreciation, depletion and amortization	26.8	25.5
Total assets (as of end of period)	1,720.9	1,805.2
Shipping and handling cost
Segment Reporting Information [Line Items]
Shipping and handling cost	80.6	91.3
Operating Segments | Salt
Segment Reporting Information [Line Items]
Sales	242.2	274.3
Operating earnings (loss)	29.4	50.9
Depreciation, depletion and amortization	17.5	15.2
Total assets (as of end of period)	1,092.4	1,056.6
Operating Segments | Salt | Shipping and handling cost
Segment Reporting Information [Line Items]
Shipping and handling cost	71.3	83.7
Operating Segments | Plant Nutrition
Segment Reporting Information [Line Items]
Sales	61.4	49.7
Operating earnings (loss)	(3.1)	(2.3)
Depreciation, depletion and amortization	7.5	8.4
Total assets (as of end of period)	388.1	469.7
Operating Segments | Plant Nutrition | Shipping and handling cost
Segment Reporting Information [Line Items]
Shipping and handling cost	9.3	7
Corporate and Other
Segment Reporting Information [Line Items]
Sales	3.6	17.7
Operating earnings (loss)	(25.8)	(102.2)
Depreciation, depletion and amortization	1.8	1.9
Total assets (as of end of period)	240.4	278.9
Corporate and Other | Shipping and handling cost
Segment Reporting Information [Line Items]
Shipping and handling cost	0	0.6
Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales	(3.2)	(3.1)
Intersegment Eliminations | Salt
Segment Reporting Information [Line Items]
Sales	0	0
Intersegment Eliminations | Plant Nutrition
Segment Reporting Information [Line Items]
Sales	$ 3.2	$ 3.1

Operating Segments - Schedule_2

Operating Segments - Schedule of Disaggregated Revenue by Product Type (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Sales to external customers	$ 307.2	$ 341.7
Production recall expense	0.9
Impairment		74.8
Severance costs		2.5
Restructuring charges		1.1
Fortress
Segment Reporting Information [Line Items]
Increase to contingent consideration liability		1.6
Highway Deicing Salt
Segment Reporting Information [Line Items]
Sales to external customers	138.1	159.4
Consumer & Industrial Salt
Segment Reporting Information [Line Items]
Sales to external customers	104.1	114.9
SOP
Segment Reporting Information [Line Items]
Sales to external customers	64.6	52.8
Fire Retardant
Segment Reporting Information [Line Items]
Sales to external customers		14
Revenue from Services
Segment Reporting Information [Line Items]
Sales to external customers		0.5
Eliminations & Other
Segment Reporting Information [Line Items]
Sales to external customers	0.4	0.1
Operating Segments | Salt
Segment Reporting Information [Line Items]
Sales to external customers	242.2	274.3
Operating Segments | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers	61.4	49.7
Operating Segments | Highway Deicing Salt | Salt
Segment Reporting Information [Line Items]
Sales to external customers	138.1	159.4
Operating Segments | Highway Deicing Salt | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Operating Segments | Consumer & Industrial Salt | Salt
Segment Reporting Information [Line Items]
Sales to external customers	104.1	114.9
Operating Segments | Consumer & Industrial Salt | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Operating Segments | SOP | Salt
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Operating Segments | SOP | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers	64.6	52.8
Operating Segments | Fire Retardant | Salt
Segment Reporting Information [Line Items]
Sales to external customers		0
Operating Segments | Fire Retardant | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers		0
Operating Segments | Revenue from Services | Salt
Segment Reporting Information [Line Items]
Sales to external customers		0
Operating Segments | Revenue from Services | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers		0
Operating Segments | Eliminations & Other | Salt
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Operating Segments | Eliminations & Other | Plant Nutrition
Segment Reporting Information [Line Items]
Sales to external customers	(3.2)	(3.1)
Corporate and Other
Segment Reporting Information [Line Items]
Sales to external customers	3.6	17.7
Corporate and Other | Highway Deicing Salt
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Corporate and Other | Consumer & Industrial Salt
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Corporate and Other | SOP
Segment Reporting Information [Line Items]
Sales to external customers	0	0
Corporate and Other | Fire Retardant
Segment Reporting Information [Line Items]
Sales to external customers		14
Corporate and Other | Revenue from Services
Segment Reporting Information [Line Items]
Sales to external customers		0.5
Corporate and Other | Eliminations & Other
Segment Reporting Information [Line Items]
Sales to external customers	$ 3.6	$ 3.2

Operating Segments - Schedule_3

Operating Segments - Schedule of Revenue by Geographic Area (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Total revenue	$ 307.2	$ 341.7
United States
Segment Reporting Information [Line Items]
Total revenue	212.7	250.9
Canada
Segment Reporting Information [Line Items]
Total revenue	79.3	77.6
United Kingdom
Segment Reporting Information [Line Items]
Total revenue	11.2	13
Other
Segment Reporting Information [Line Items]
Total revenue	$ 4	$ 0.2

Stockholders' Equity and Equi_3

Stockholders' Equity and Equity Instruments - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Mar. 31, 2024	Feb. 28, 2022	Dec. 31, 2024	Dec. 31, 2023	May 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury stock reissued (in shares)			222,155
Tax deficiency from equity compensation awards recorded as an increase to income tax expense			$ 0.5
Share-based payment arrangement, expense			$ 3.9	$ 11.9
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reissued share of treasury stock (in shares)			108,023
Stock Payments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reissued share of treasury stock (in shares)			10,224
Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld related to vesting of RSUs and PSUs (in shares)			34,955
Fair value of stock withheld related to vesting of RSUs and PSUs			$ 0.5
Scorecard PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period			3 years
Modifier change			20%
Scorecard PSUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation payment award performance percentage			0%
Scorecard PSUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation payment award performance percentage			200%
2020 Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for issuance (in shares)					2,977,933
Shares authorized for issuance (in shares)	3,000,000	750,000

Stockholders' Equity and Equi_4

Stockholders' Equity and Equity Instruments - Schedule of Stock-Based Compensation Activity (Details)	3 Months Ended
	Dec. 31, 2024 $ / shares shares
Stock Options
Number
Outstanding at beginning of period (in shares)	187,023
Granted (in shares)	0
Exercised (in shares)	0
Released from restriction (in shares)	0
Cancelled/expired (in shares)	(3,279)
Outstanding at end of period (in shares)	183,744
Weighted-average exercise price
Weighted-average exercise price at beginning of period (in dollars per share) | $ / shares	$ 62.85
Weighted-average exercise price, granted (in dollars per share) | $ / shares	0
Weighted-average exercise price, exercised (in dollars per share) | $ / shares	0
Weighted-average exercise price, released from restriction (in dollars per share) | $ / shares	0
Weighted-average exercise price, cancelled/expired (in dollars per share) | $ / shares	64.12
Weighted-average exercise price at end of period (in dollars per share) | $ / shares	$ 62.83
RSUs
Number
Outstanding at beginning of period (in shares)	451,091
Granted (in shares)	749,627
Exercised (in shares)	0
Released from restriction (in shares)	(108,023)
Cancelled/expired (in shares)	(5,843)
Outstanding at end of period (in shares)	1,086,852
Weighted-average fair value
Weighted-average fair value at beginning of period (in dollars per share) | $ / shares	$ 27.93
Weighted-average fair value, granted (in dollars per share) | $ / shares	12.83
Weighted-average fair value, exercised (in dollars per share) | $ / shares	0
Weighted-average fair value, released from restriction (in dollars per share) | $ / shares	32.70
Weighted-average fair value, cancelled/expired (in dollars per share) | $ / shares	18.03
Weighted-average fair value at end of period (in dollars per share) | $ / shares	$ 17.09
PSUs
Number
Outstanding at beginning of period (in shares)	229,469
Granted (in shares)	214,673
Exercised (in shares)	0
Released from restriction (in shares)	0
Cancelled/expired (in shares)	0
Outstanding at end of period (in shares)	444,142
Weighted-average fair value
Weighted-average fair value at beginning of period (in dollars per share) | $ / shares	$ 40.26
Weighted-average fair value, granted (in dollars per share) | $ / shares	16.57
Weighted-average fair value, exercised (in dollars per share) | $ / shares	0
Weighted-average fair value, released from restriction (in dollars per share) | $ / shares	0
Weighted-average fair value, cancelled/expired (in dollars per share) | $ / shares	0
Weighted-average fair value at end of period (in dollars per share) | $ / shares	$ 28.81
PSU at grant date (in shares per unit)	1

Stockholders' Equity and Equi_5

Stockholders' Equity and Equity Instruments - Schedule of Components and Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 316.6	$ 521
Other comprehensive (loss) income before reclassifications	(34.2)	12
Amounts reclassified from AOCL	0.7	1
Net current period other comprehensive income (loss)	(33.5)	13
Ending balance	263	463.4
Gain (loss) on foreign exchange of intercompany notes of long-term nature	5.4	(2.3)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(96.4)	(104.7)
Ending balance	(129.9)	(91.7)
Gains and (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1.3)	(1.4)
Other comprehensive (loss) income before reclassifications	(0.9)	(2.6)
Amounts reclassified from AOCL	0.6	0.8
Net current period other comprehensive income (loss)	(0.3)	(1.8)
Ending balance	(1.6)	(3.2)
Benefit Plans | Defined Benefit Pension
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(6.2)	(6.6)
Other comprehensive (loss) income before reclassifications	0	0
Amounts reclassified from AOCL	0.2	0.2
Net current period other comprehensive income (loss)	0.2	0.2
Ending balance	(6)	(6.4)
Benefit Plans | Other Post-Employment Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	1.4	1.7
Other comprehensive (loss) income before reclassifications	0	0
Amounts reclassified from AOCL	(0.1)	0
Net current period other comprehensive income (loss)	(0.1)	0
Ending balance	1.3	1.7
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(90.3)	(98.4)
Other comprehensive (loss) income before reclassifications	(33.3)	14.6
Amounts reclassified from AOCL	0	0
Net current period other comprehensive income (loss)	(33.3)	14.6
Ending balance	$ (123.6)	$ (83.8)

Stockholders' Equity and Equi_6

Stockholders' Equity and Equity Instruments - Schedule of Amounts Reclassified from AOCL to Expense (Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax benefit (expense)	$ 9.7	$ 3.6
Reclassifications, net of income taxes	(23.6)	(75.3)
Product cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product cost	(192.3)	(179.3)
Amount Reclassified from AOCL
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of income taxes	0.7	1
Amount Reclassified from AOCL | Loss (gain) on cash flow hedges:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax benefit (expense)	0	0
Reclassifications, net of income taxes	0.6	0.8
Amount Reclassified from AOCL | Loss (gain) on cash flow hedges: | Natural gas instruments | Product cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product cost	0.6	0.8
Amount Reclassified from AOCL | Amortization of defined benefit pension:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax benefit (expense)	(0.1)	(0.1)
Reclassifications, net of income taxes	0.2	0.2
Amount Reclassified from AOCL | Amortization of defined benefit pension: | Product cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product cost	0.3	0.3
Amount Reclassified from AOCL | Amortization of other post-employment benefits:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax benefit (expense)	0	0
Reclassifications, net of income taxes	(0.1)	0
Amount Reclassified from AOCL | Amortization of other post-employment benefits: | Product cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product cost	$ (0.1)	$ 0

Derivative Financial Instrume_3

Derivative Financial Instruments - Narrative (Details) MMBTU in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2024 USD ($) MMBTU	Sep. 30, 2024 MMBTU
Derivatives, Fair Value [Line Items]
Net gains to be reclassified from accumulated other comprehensive loss to earnings during the next 12 months | $	$ 1.7
Natural gas instruments
Derivatives, Fair Value [Line Items]
Notional amount (in MMBtus) | MMBTU	2.6	2.3
Natural gas instruments | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Percent of forecasted usage to be hedged	90%
Maximum period which the company hedges in advance of forecasted purchase	36 months

Derivative Financial Instrume_4

Derivative Financial Instruments - Schedule of Fair Value of Derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 0.6	$ 0.6
Liability Derivatives	2.2	1.9
Natural gas instruments
Derivatives, Fair Value [Line Items]
Netting of contracts in a receivable position against contracts in payable position	0.6	0.6
Natural gas instruments | Derivatives Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.3	0.5
Natural gas instruments | Derivatives Designated as Hedging Instruments | Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	2	1.7
Natural gas instruments | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.3	0.1
Natural gas instruments | Derivatives Designated as Hedging Instruments | Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0.2	$ 0.2

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Estimated Fair Values for Type of Instrument (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024
Asset Class:
Mutual fund investments in a non-qualified savings plan	$ 3.4	$ 3.1
Total Assets	4	3.7
Liability Class:
Liabilities related to non-qualified savings plan	(3.4)	(3.1)
Total Liabilities	(5.6)	(5)
Natural Gas Instruments, Net
Asset Class:
Derivatives - natural gas instruments, net	0.6	0.6
Liability Class:
Derivative liabilities	$ (2.2)	$ (1.9)
Common Stock, Large Cap US Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	25%	35%
Common Stock of Small to Mid Cap US Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	5%	5%
Common Stock, International Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)		5%
Bond Funds | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	10%	10%
Short-Term Investments | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	20%	5%
Blended Funds | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	40%	40%
Level One
Asset Class:
Mutual fund investments in a non-qualified savings plan	$ 3.4	$ 3.1
Total Assets	3.4	3.1
Liability Class:
Liabilities related to non-qualified savings plan	(3.4)	(3.1)
Total Liabilities	(3.4)	(3.1)
Level One | Natural Gas Instruments, Net
Asset Class:
Derivatives - natural gas instruments, net	0	0
Liability Class:
Derivative liabilities	0	0
Level Two
Asset Class:
Mutual fund investments in a non-qualified savings plan	0	0
Total Assets	0.6	0.6
Liability Class:
Liabilities related to non-qualified savings plan	0	0
Total Liabilities	(2.2)	(1.9)
Level Two | Natural Gas Instruments, Net
Asset Class:
Derivatives - natural gas instruments, net	0.6	0.6
Liability Class:
Derivative liabilities	(2.2)	(1.9)
Level Three
Asset Class:
Mutual fund investments in a non-qualified savings plan	0	0
Total Assets	0	0
Liability Class:
Liabilities related to non-qualified savings plan	0	0
Total Liabilities	0	0
Level Three | Natural Gas Instruments, Net
Asset Class:
Derivatives - natural gas instruments, net	0	0
Liability Class:
Derivative liabilities	$ 0	$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions		3 Months Ended
	May 05, 2023	Dec. 31, 2023	Dec. 31, 2024	Sep. 30, 2024
Debt Instrument [Line Items]
Mutual fund investments in a non-qualified savings plan			$ 3.4	$ 3.1
Contingent consideration, liability			$ 7.9	$ 7.9
Fortress
Debt Instrument [Line Items]
Contingent consideration, liability	$ 28
Performance period	5 years
Contingent consideration period	10 years
Increase to contingent consideration liability		$ 1.6
Senior Notes | 6.75% Senior Notes due December 2027
Debt Instrument [Line Items]
Stated interest rate			6.75%	6.75%
Fair value of senior notes			$ 492.5	$ 497
Senior Notes Due 2027
Debt Instrument [Line Items]
Debt fair value amount			500	500
Term Loan
Debt Instrument [Line Items]
Fair value of credit agreement debt			416.8	379.1
Aggregate principal amount due at maturity			422.1	383.9
Fair Value, Measurements, Recurring
Debt Instrument [Line Items]
Mutual fund investments in a non-qualified savings plan			$ 3.4	$ 3.1

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Total Contingent Consideration (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Accrued expenses and other current liabilities	$ 0.1	$ 0
Other noncurrent liabilities	7.8	7.9
Total contingent consideration	$ 7.9	$ 7.9

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Numerator:
Net loss	$ (23.6)	$ (75.3)
Less: net earnings allocated to participating securities	0	(0.1)
Net (loss) earnings available to common stockholders, basic	(23.6)	(75.4)
Net (loss) earnings available to common stockholders, diluted	$ (23.6)	$ (75.4)
Denominator (in thousands):
Weighted-average common shares outstanding, shares for basic earnings per share (in shares)	41,441	41,205
Weighted-average awards outstanding (in shares)	0	0
Shares for diluted earnings per share (in shares)	41,441	41,205
Basic net (loss) earnings per common share (in dollars per share)	$ (0.57)	$ (1.83)
Diluted net (loss) earnings per common share (in dollars per share)	$ (0.57)	$ (1.83)
Participating securities (in shares)	1,116,000	777,000
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted options outstanding (in shares)	1,184,000	1,572,000

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Sep. 30, 2024
Related Party Transaction [Line Items]
Total revenue	$ 307,200,000	$ 341,700,000
Receivables	261,700,000		$ 126,100,000
Accounts payable	96,200,000		82,100,000
Koch Minerals & Trading, LLC
Related Party Transaction [Line Items]
Total revenue	1,100,000	$ 800,000
Receivables	600,000		$ 300,000
Accounts payable	$ 0