Compass Minerals International (CMP) 10-Q 15 May 24 2024 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Mar. 31, 2024	May 10, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 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	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		41,333,826
Entity Central Index Key	0001227654
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023
Current assets:
Cash and cash equivalents	$ 40	$ 38.7
Receivables, less allowance for doubtful accounts of $2.2 at March 31, 2024 and $2.3 at September 30, 2023	143	129.5
Inventories	367.7	392.2
Other	47.4	33.4
Total current assets	598.1	593.8
Property, plant and equipment, net	793.5	852.2
Intangible assets, net	102	120
Goodwill	5.9	96.8
Other	152.6	155.2
Total assets	1,652.1	1,818
Current liabilities:
Current portion of long-term debt	5	5
Accounts payable	88.5	116.8
Accrued salaries and wages	18.7	25.7
Income taxes payable	13.9	16.5
Accrued interest	12.9	12.9
Accrued expenses and other current liabilities	61.9	98.9
Total current liabilities	200.9	275.8
Long-term debt, net of current portion	872.2	800.3
Deferred income taxes, net	59.6	58.5
Other noncurrent liabilities	131.7	166.2
Commitments and contingencies
Stockholders’ equity:
Common stock: $0.01 par value, 200,000,000 authorized shares; 42,197,964 issued shares at March 31, 2024 and September 30, 2023	0.4	0.4
Additional paid-in capital	419.7	413.1
Treasury stock, at cost — 865,027 shares at March 31, 2024 and 1,038,168 shares at September 30, 2023	(10.1)	(8.7)
Retained earnings	81.3	217.1
Accumulated other comprehensive loss	(103.6)	(104.7)
Total stockholders’ equity	387.7	517.2
Total liabilities and stockholders’ equity	$ 1,652.1	$ 1,818

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023
ASSETS
Allowance for doubtful accounts	$ 2.2	$ 2.3
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)	865,027	1,038,168

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Sales	$ 364	$ 411.1	$ 705.7	$ 763.5
Gross profit	72.9	85.2	143.5	155.2
Selling, general and administrative expenses	33.3	34.4	79	76.2
Loss on impairments	106.6	0	181.4	0
Other operating (income) expense	(21.2)	2.9	(15.8)	3.2
Operating (loss) earnings	(45.8)	47.9	(101.1)	75.8
Other (income) expense:
Interest income	(0.2)	(1.9)	(0.6)	(3)
Interest expense	17.1	14.2	32.9	28.1
(Gain) loss on foreign exchange	(2.5)	(0.2)	(0.6)	2.3
Net loss in equity investee	0	1.4	0	2.3
Other expense, net	0.9	0.9	1.6	1
(Loss) earnings before income taxes	(61.1)	33.5	(134.4)	45.1
Income tax (benefit) expense	(13.1)	55.1	(11.3)	67
Net loss	$ (48)	$ (21.6)	$ (123.1)	$ (21.9)
Basic net loss per common share (in dollars per share)	$ (1.16)	$ (0.53)	$ (2.99)	$ (0.55)
Diluted net loss per common share (in dollars per share)	$ (1.16)	$ (0.53)	$ (2.99)	$ (0.55)
Weighted-average common shares outstanding (in thousands):
Basic (in shares)	41,306	41,110	41,255	40,423
Diluted (in shares)	41,306	41,110	41,255	40,423
Shipping and handling cost
Cost	$ 110.6	$ 130.1	$ 201.9	$ 237.5
Product cost
Cost	$ 180.5	$ 195.8	$ 360.3	$ 370.8

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (48)	$ (21.6)	$ (123.1)	$ (21.9)
Other comprehensive income (loss):
Unrealized gain from change in pension obligations, net of tax of $(0.1) and $0.0 for the three months ended March 31, 2024 and 2023, respectively, and $(0.2) and $0.0 for the six months ended March 31, 2024 and 2023, respectively	0.2	0	0.4	0.1
Unrealized income (loss) on cash flow hedges, net of tax of $0.0 for the three months ended March 31, 2024 and 2023, and $0.0 and $0.4 for the six months ended March 31, 2024 and 2023, respectively	0.6	(1.1)	(1.2)	(3.9)
Cumulative translation adjustment	(12.7)	2.8	1.9	14.5
Comprehensive loss	$ (59.9)	$ (19.9)	$ (122)	$ (11.2)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Unrealized gain from change in pension obligations, tax	$ (0.1)	$ 0	$ (0.2)	$ 0
Unrealized gain (loss) on cash flow hedges, tax	$ 0		$ 0	$ 0.4

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Sep. 30, 2022	$ 256.4	$ 0.4	$ 152.1		$ 226.5	$ (115.3)
Beginning balance, treasury stock at Sep. 30, 2022				$ (7.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive (loss) income	8.7				(0.3)	9
Dividends on common stock	(6.3)				(6.3)
Private placement of common stock	240.7		240.7
Shares issued for stock units, net of shares withheld for taxes	(0.3)			(0.3)
Stock-based compensation	10.6		10.6
Ending balance at Dec. 31, 2022	509.8	0.4	403.4		219.9	(106.3)
Ending balance , treasury stock at Dec. 31, 2022				(7.6)
Beginning balance at Sep. 30, 2022	256.4	0.4	152.1		226.5	(115.3)
Beginning balance, treasury stock at Sep. 30, 2022				(7.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive (loss) income	(11.2)
Ending balance at Mar. 31, 2023	485.4	0.4	406.2		192	(104.6)
Ending balance , treasury stock at Mar. 31, 2023				(8.6)
Beginning balance at Dec. 31, 2022	509.8	0.4	403.4		219.9	(106.3)
Beginning balance, treasury stock at Dec. 31, 2022				(7.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive (loss) income	(19.9)				(21.6)	1.7
Dividends on common stock	(6.3)				(6.3)
Shares issued for stock units, net of shares withheld for taxes	(1.3)		(0.3)	(1)
Stock-based compensation	3.1		3.1
Ending balance at Mar. 31, 2023	485.4	0.4	406.2		192	(104.6)
Ending balance , treasury stock at Mar. 31, 2023				(8.6)
Beginning balance at Sep. 30, 2023	517.2	0.4	413.1		217.1	(104.7)
Beginning balance, treasury stock at Sep. 30, 2023	(8.7)			(8.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive (loss) income	(62.1)				(75.1)	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	459.8	0.4	424.8		135.6	(91.7)
Ending balance , treasury stock at Dec. 31, 2023				(9.3)
Beginning balance at Sep. 30, 2023	517.2	0.4	413.1		217.1	(104.7)
Beginning balance, treasury stock at Sep. 30, 2023	(8.7)			(8.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive (loss) income	(122)
Ending balance at Mar. 31, 2024	387.7	0.4	419.7		81.3	(103.6)
Ending balance , treasury stock at Mar. 31, 2024	(10.1)			(10.1)
Beginning balance at Dec. 31, 2023	459.8	0.4	424.8		135.6	(91.7)
Beginning balance, treasury stock at Dec. 31, 2023				(9.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive (loss) income	(59.9)				(48)	(11.9)
Dividends on common stock	(6.3)				(6.3)
Shares issued for stock units, net of shares withheld for taxes	(1)		(0.2)	(0.8)
Stock-based compensation	(4.9)		(4.9)
Ending balance at Mar. 31, 2024	387.7	$ 0.4	$ 419.7		$ 81.3	$ (103.6)
Ending balance , treasury stock at Mar. 31, 2024	$ (10.1)			$ (10.1)

CONSOLIDATED STATEMENTS OF ST_2

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Statement of Stockholders' Equity [Abstract]
Cash dividends per share (in dollars per share)	$ 0.15	$ 0.15	$ 0.15	$ 0.15

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net loss	$ (123.1)	$ (21.9)
Adjustments to reconcile net loss to net cash flows provided by operating activities:
Depreciation, depletion and amortization	52.3	48.4
Amortization of deferred financing costs	1.2	1.5
Stock-based compensation	7	13.7
Deferred income taxes	0.8	(4.2)
Unrealized foreign exchange (gain) loss	(0.7)	2.3
Loss on impairments	181.4	0
Net loss in equity investees	0	2.3
Net gain from remeasurement of contingent consideration	(21.4)	0
Other, net	2	2.4
Changes in operating assets and liabilities:
Receivables	(12.7)	8.9
Inventories	26.7	44.1
Other assets	(10.3)	18.4
Accounts payable and accrued expenses and other current liabilities	(71.2)	41.2
Other liabilities	(9.7)	(7.6)
Net cash provided by operating activities	22.3	149.5
Cash flows from investing activities:
Capital expenditures	(65.3)	(49.3)
Other, net	(1.1)	(0.3)
Net cash used in investing activities	(66.4)	(49.6)
Cash flows from financing activities:
Proceeds from revolving credit facility borrowings	217.2	16.7
Principal payments on revolving credit facility borrowings	(176.5)	(168.2)
Proceeds from issuance of long-term debt	69.4	37.5
Principal payments on long-term debt	(38)	(9.1)
Payments for contingent consideration	(9.1)	0
Net proceeds from private placement of common stock	0	240.7
Dividends paid	(12.7)	(12.6)
Deferred financing costs	(2.1)	0
Shares withheld to satisfy employee tax obligations	(1.8)	(1.6)
Other, net	(1.1)	(0.5)
Net cash provided by financing activities	45.3	102.9
Effect of exchange rate changes on cash and cash equivalents	0.1	0.8
Net change in cash and cash equivalents	1.3	203.6
Cash and cash equivalents, beginning of the year	38.7	46.1
Cash and cash equivalents, end of period	40	249.7
Supplemental cash flow information:
Interest paid, net of amounts capitalized	31.5	26.5
Income taxes paid, net of refunds	$ 22.1	$ 14

Accounting Policies and Basis o

Accounting Policies and Basis of Presentation	6 Months Ended
	Mar. 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 working to develop next-generation, environmentally friendly fire retardants to help to slow, stop and prevent wildfires. Additionally, the Company had been pursuing the development of a sustainable lithium salt resource to support the North American battery market. However, as described in Note 5 , the Company has terminated its pursuit of the lithium development. 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, 2023, as filed with the Securities and Exchange Commission (the “SEC”) in its Annual Report on Form 10-K on November 29, 2023 (“2023 Form 10-K”). Certain amounts in prior periods have been reclassified to conform to the current period presentation. 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, the 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. Revision of Previously Issued Financial Statements The Company identified certain misstatements in the historical presentation of its Consolidated Statements of Cash Flows. The misstatements were the result of the Company not reflecting the appropriate amount of non-cash capital expenditures in accounts payable in its operating and investing cash flows and had no effect on the Company’s Consolidated Balance Sheets or its Consolidated Statements of Operations. Management has considered the misstatements, and after evaluating both their quantitative and qualitative impacts, concluded they are not material to the Company’s previously issued consolidated financial statements. To correct the immaterial misstatements, the Company has revised its Consolidated Statements of Cash Flows for the interim period ended March 31, 2023 and the interim period ended December 31, 2023. Certain prior period amounts have been reclassified to conform to the current period presentation. For further detail, refer to Note 16 . Impairments As a result of a sustained decrease in the Company’s publicly quoted share price and market capitalization continuing into fiscal 2024 and recent developments related to its magnesium chloride-based fire retardants impacting its Fortress business, the Company determined that there were indicators of impairment and therefore performed long-lived assets and goodwill impairment testing. The analysis for Plant Nutrition resulted in no long-lived asset impairment but did result in a goodwill impairment, as discussed further below. The Fortress analysis resulted in an impairment of the Company’s magnesium chloride-related assets and goodwill; see below for additional details. On March 22, 2024, the Company was notified of the decision by the U.S. Forest Service that the Company would not be awarded a contract to supply its magnesium chloride-based aerial fire retardant for the calendar 2024 fire season. For purposes of the long-lived asset impairment evaluation, management grouped and tested the magnesium chloride-related assets given their unique classification and separately identifiable cash flows. As a result of the evaluation using the income approach, the Company impaired all magnesium chloride-related assets which resulted in a long-lived asset, net, impairment of $15.6 million (finite-lived intangible assets) and an impairment of $1.5 million of finished goods inventory for the three and six months ended March 31, 2024. The long-lived asset impairment is included in loss on impairments, while the inventory impairment is reflected in product cost, both on the Consolidated Statements of Operations. The undiscounted cash flows for the remaining Fortress assets were greater than their carrying value resulting in no incremental impairment. Management will continue to monitor events and circumstances that would require a future test of recoverability on the remaining Fortress long-lived assets. The Company performed the interim goodwill impairment tests consistent with its approach for annual impairment testing, including using similar models, inputs and assumptions. As a result of the interim goodwill impairment test, the Company recognized impairment charges totaling $91.0 million included in loss on impairments, on the Consolidated Statements of Operations for both the three and six months ended March 31, 2024. Goodwill impairment of $51.0 million was related to the Company’s Plant Nutrition segment, primarily due to decreases in projected future revenues and cash flows and an increase in discount rates due to the uncertain regulatory environment in Utah. The remaining goodwill impairment of $40.0 million was related to the Company’s Fortress reporting unit (included in the Corporate and Other segment), primarily due to changes in assumptions surrounding the magnesium chloride-based fire retardants which impacted projected future revenues and cash flows. Following the impairment charges, there is no remaining goodwill balance for the Plant Nutrition and Fortress reporting units. Refer to Note 6 for a summary of goodwill by segment. A summary of the impairments incurred for the three and six months ended March 31, 2024, is detailed below (in millions): Impairment Financial Statement Line Item Segment Three Months Ended Six Months Ended Lithium long-lived assets, net Loss on impairments Corporate & Other $ — $ 74.8 Plant Nutrition goodwill Loss on impairments Plant Nutrition 51.0 51.0 Fortress goodwill Loss on impairments Corporate & Other 40.0 40.0 Fortress long-lived assets, net Loss on impairments Corporate & Other 15.6 15.6 Fortress inventory Product cost Corporate & Other 1.5 1.5 Total $ 108.1 $ 182.9 In connection with the aforementioned impairments, the Company determined the estimated fair value for each reporting unit based on discounted cash flow projections (income approach), market values for comparable businesses (market approach) or a combination of both. Under the income approach, the Company is required to make judgments about appropriate discount rates, long-term revenue growth rates and the amount and timing of expected future cash flows. The cash flows used in its estimates are based on the reporting unit's forecast, long-term business plan, and recent operating performance. Discount rate assumptions are based on an assessment of the risk inherent in the future cash flows of the respective reporting unit and market conditions. The Company’s estimates may differ from actual future cash flows. The risk adjusted discount rate used is consistent with the weighted average cost of capital of the Company’s peer companies and is intended to represent a rate of return that would be expected by a market participant. Under the market approach, market multiples are derived from market prices of stocks of companies in the Company’s peer group. The appropriate multiple is applied to the forecasted revenue and earnings before interest, taxes, depreciation and amortization of the reporting unit to obtain an estimated fair value. The most critical assumptions used in the calculation of the fair value of each reporting unit are the projected revenue growth rates, long-term operating margin, terminal growth rates, discount rate, and the selection of market multiples. The projected long term operating margin utilized in the Company’s fair value estimates is consistent with the its operating plan and is dependent on the successful execution of its long-term business plan, overall industry growth rates and the competitive environment. The discount rate could be adversely impacted by changes in the macroeconomic environment and volatility in the equity and debt markets. Although management believes its estimate of fair value is reasonable, if the future financial performance falls below expectations or there are unfavorable revisions to significant assumptions, or if the Company’s market capitalization declines, an additional non-cash goodwill impairment charge may be required in a future period. Management does not believe that the remaining goodwill balance in its Corporate and Other reporting unit is currently at risk of impairment as of March 31, 2024. 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 2023 Form 10-K. There were no material changes in the Company’s significant accounting policies from those described in its 2023 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.

Business Acquisition

Business Acquisition	6 Months Ended
	Mar. 31, 2024
Business Combination and Asset Acquisition [Abstract]
Business Acquisition	Business Acquisition: Beginning in 2020, the Company began a series of equity investments in Fortress, a next-generation fire retardant business dedicated to developing and producing a portfolio of fire retardant products to help combat wildfires. On May 5, 2023, the Company acquired the remaining 55% interest in Fortress not previously owned in exchange for an initial cash payment of $18.9 million (net of cash held by Fortress of $6.5 million), and additional contingent consideration of 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. Building upon the previous 45% minority ownership stake in Fortress, the transaction provided the Company full ownership of all Fortress assets, contracts, and intellectual property. See Note 1 for impairment information. See Note 13 for fair value information related to the contingent consideration as of March 31, 2024.

Revenues

Revenues	6 Months Ended
	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenues	Revenues: Deferred Revenue Deferred revenue represents billings 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 March 31, 2024 and September 30, 2023 was approximately $4.1 million and $8.5 million, respectively. See Note 10 for a disaggregation of sales by segment, type and geographical region.

Inventories

Inventories	6 Months Ended
	Mar. 31, 2024
Inventory Disclosure [Abstract]
Inventories	Inventories: Inventories consist of the following (in millions): March 31, September 30, Finished goods $ 278.6 $ 319.3 Raw materials and supplies 89.1 72.9 Total inventories $ 367.7 $ 392.2

Property, Plant and Equipment,

Property, Plant and Equipment, Net	6 Months Ended
	Mar. 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): March 31, September 30, Land, buildings and structures, and leasehold improvements $ 550.4 $ 547.9 Machinery and equipment 1,131.4 1,102.0 Office furniture and equipment 22.3 21.6 Mineral interests 169.6 169.1 Construction in progress 60.2 113.0 1,933.9 1,953.6 Less: accumulated depreciation and depletion (1,140.4) (1,101.4) Property, plant and equipment, net $ 793.5 $ 852.2 The Company had been pursuing the development of a sustainable lithium salt resource to support the North American battery market. The passage of Utah House Bill 513 in March 2023 and the subsequent rulemaking process altered certain aspects of the regulatory landscape that will govern the development of lithium at the Great Salt Lake, introducing uncertainty into how development would proceed. As previously disclosed in the Company’s 2023 Form 10-K, the Company indefinitely paused new investment in its lithium development project pending greater clarity on the evolving regulatory environment in Utah. In December of 2023, a revised draft of the aforementioned rulemaking was published that continued to be, in the Company's assessment, adverse to its lithium development project. In addition, in December of 2023, the Company further refined its engineering estimates that, taken together with the proposed rules and decline in market price for lithium products, would result in inadequate risk-adjusted returns on capital. On January 23, 2024, the Company severed certain members of its lithium development team and terminated its pursuit of the lithium development. Consequently, the Company evaluated the capitalized assets, including site preparation, project engineering, equipment and materials and capitalized labor and interest. As a result, the Company has recorded an impairment charge of $74.8 million for the six months ended March 31, 2024, including $5.9 million associated with future commitments as of March 31, 2024. Additional restructuring charges of $1.7 million were also recorded in other operating (income) expense during the three months ended March 31, 2024. The impairments were recorded to reflect the assets at their estimated fair value, considering equipment expected to be used by the on-going business and amounts estimated to be recoverable through returns or salvage value. Prior to recognizing an impairment, the Company had capitalized $72.7 million to its property, plant and equipment on its Consolidated Balance Sheet and has approximately $5.1 million remaining as of March 31, 2024, included in inventory. The Company engaged a valuation specialist to assist in determining the appropriate fair value of the lithium assets and the resulting impairment charge in the first quarter of fiscal 2024. Given the assets are likely to either be used in other operations or liquidated at a later date, the Company utilized a market-based approach that relied on Level 3 inputs (see Note 13

Goodwill and Intangible Assets

Goodwill and Intangible Assets	6 Months Ended
	Mar. 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): Plant Nutrition Corporate & Other Consolidated Balance as of September 30, 2023 $ 51.1 $ 45.7 $ 96.8 Foreign currency translation adjustment 0.2 0.2 0.4 Balance as of December 31, 2023 $ 51.3 $ 45.9 $ 97.2 Foreign currency translation adjustment (0.3) — (0.3) Impairments (51.0) (40.0) (91.0) Balance as of March 31, 2024 $ — $ 5.9 $ 5.9 As of March 31, 2024, there were indicators necessitating an interim impairment test of the Company’s goodwill based on the Company’s review of its operating performance, among other factors, for the relevant reporting units. Refer to Note 1 for additional details. In addition to the Plant Nutrition and Fortress impairments, the remaining change in goodwill between September 30, 2023, and March 31, 2024 was due to the impact from translating foreign-denominated amounts to U.S. dollars. In connection with the Fortress acquisition described in Note 2 , the Company acquired identifiable intangible assets which consisted of customer relationships, developed technology, in-process research and development and trade name. The fair values were determined using Level 3 inputs (see Note 13 for a discussion of the levels in the fair value hierarchy). Upon acquisition, the fair value of the customer relationships was estimated using an income approach method while the fair values of developed technology, in-process research and development and trade name were estimated using the relief from royalty method. As a result of the Fortress-related impairments discussed in Note 1 , the Company impaired all magnesium chloride-related assets which resulted in an impairment of the Company’s developed technology intangible asset of $15.6 million, net of accumulated amortization of $0.4 million. The Company continues to have Fortress-related net intangible assets consisting of customer relationships and trade name of $55.2 million and $0.2 million, respectively, as of March 31, 2024. The Company also has $2.2 million of indefinite-lived in-process research and development recognized in connection with the Fortress acquisition as of March 31, 2024, which will be reviewed for impairment at least annually, or in the event of indicators of impairment, until product development is completed.

Income Taxes

Income Taxes	6 Months Ended
	Mar. 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. 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 March 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 six months ended March 31, 2024, an additional valuation allowance of $28.3 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 estimates of future taxable income during the carryforward period are increased or reduced or 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 March 31, 2024, and September 30, 2023, the Company had $65.5 million and $65.4 million, respectively of gross foreign federal NOL carryforwards that have no expiration date and $2.9 million at March 31, 2024 and September 30, 2023 of net operating tax-effected state NOL carryforwards which expire beginning in 2035. 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 2002-2018. The reassessments are a result of ongoing audits and total $188.7 million, including interest, through March 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 $161.9 million performance bond and has paid $36.7 million to the Canadian tax authorities (most of which is recorded in other assets in the Consolidated Balance Sheets at March 31, 2024, and September 30, 2023), 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 March 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 2023 Form10-K.

Long-Term Debt

Long-Term Debt	6 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt: Long-term debt consists of the following (in millions): March 31, September 30, 6.75% Senior Notes due December 2027 $ 500.0 $ 500.0 Term Loan due May 2028 196.3 198.8 Revolving Credit Facility due May 2028 122.2 81.5 AR Securitization Facility expires March 2027 64.8 30.9 883.3 811.2 Less unamortized debt issuance costs (6.1) (5.9) Total debt 877.2 805.3 Less current portion (5.0) (5.0) Long-term debt $ 872.2 $ 800.3 On March 27, 2024, the Company entered into an amendment to its 2023 Credit Agreement, which 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 6.0x as of the fiscal quarter ended March 31, 2024, increasing further to 6.5x as of the last day of any quarter through the fiscal quarter ended December 31, 2024, then gradually stepping down to 4.75x by the fiscal quarter ended March 31, 2026 and thereafter. The amendment also removed the flexibility related to the lithium development joint ventures, projects or similar arrangements and any related funding transactions in connection therewith. In connection with this amendment, the Company paid fees totaling $1.7 million which were capitalized as deferred financing costs. Additional arrangement and legal fees of $0.9 million were expensed as of March 31, 2024. On March 27, 2024, certain of the Company’s U.S. subsidiaries entered into an amendment to its revolving accounts receivable financing facility with PNC Bank, National Association, extending the facility to March 2027. In connection with this amendment, the Company paid fees totaling $0.4 million which were capitalized as deferred financing costs. As of March 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 March 31, 2024 and September 30, 2023, the weighted average interest rate on all borrowings outstanding under the 2023 Credit Agreement was approximately 8.4% and 7.8%, 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 8.2% and 10.3% as of March 31, 2024, and 7.7% and 9.8% as of September 30, 2023. As of March 31, 2024, the Company had $237.7 million of availability under its $375 million revolving credit facility. 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 March 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	6 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies: As previously disclosed, the Company was the subject of an investigation by the Division of Enforcement of the SEC regarding the Company’s disclosures primarily concerning the operation of the Goderich mine, the former South American businesses, and related accounting and internal control matters including Salt interim inventory valuation methodology issues that were disclosed in the Company’s Form 10-K/A for the year ended December 31, 2020, and Form 10-Q/A for the quarter ended March 31, 2021, each filed with the SEC on September 3, 2021. On September 23, 2022, the Company reached a settlement with the SEC, concluding and resolving the SEC investigation in its entirety. Under the terms of the settlement, the Company, without admitting or denying the findings in the administrative order issued by the SEC, agreed to pay a civil penalty of $12 million and to cease and desist from violations of specified provisions of the federal securities laws and rules promulgated thereunder, and to retain an independent compliance consultant for a period of approximately one year to review certain accounting practices and procedures. As set forth in the administrative order, the $12 million civil penalty was paid in installments with $10 million reflected in accrued expenses and other current liabilities on the Company’s Consolidated Balance Sheets as of September 30, 2023 and subsequently paid in during the first quarter of fiscal 2024. On April 24, 2024, the Company, one of its former officers and three current officers were named as defendants in a punitive securities class action lawsuit filed in the United States District Court for the District of Kansas, alleging that the Company and such officers made misleading statements damaging shareholders relating to the Company’s fire retardant business. The Company intends to vigorously defend these allegations. At this time, the Company is unable to assess with any certainty what, if any, damages could be awarded in this matter. On May 1, 2024, Fortress was named as defendant in a trade secrets lawsuit filed by Perimeter Solutions L.P. in the United States District Court for the Eastern District of California, alleging that certain of Fortress’s non-magnesium chloride fire retardant products were developed using Perimeter’s trade secrets, and seeking unspecified damages (including exemplary damages) and injunctive relief. The Company intends to vigorously defend these allegations. At this time, the Company is unable to assess with any certainty what, if any, damages could be awarded in this matter. On May 1, 2024, Perimeter Solutions L.P. also filed a lawsuit in the United States District Court for the Eastern District of Missouri alleging similar claims against an employee of Fortress for breach of contract and misappropriation of trade secrets. 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 7 and this Note 9.

Operating Segments

Operating Segments	6 Months Ended
	Mar. 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 and six months ended March 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. Refer to Note 2 for a discussion of the acquisition of the fire retardant business. Segment information is as follows (in millions): Three Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Sales to external customers $ 310.4 $ 50.1 $ 3.5 $ 364.0 Intersegment sales — 0.7 (0.7) — Shipping and handling cost 104.0 6.6 — 110.6 Operating earnings (loss) (b)(c)(d) 66.4 (53.4) (58.8) (45.8) Depreciation, depletion and amortization 16.2 8.7 1.9 26.8 Total assets (as of end of period) 998.4 416.0 237.7 1,652.1 Three Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Sales to external customers $ 360.5 $ 47.7 $ 2.9 $ 411.1 Intersegment sales — 1.4 (1.4) — Shipping and handling cost 124.0 6.1 — 130.1 Operating earnings (loss) (c)(d) 73.1 (0.7) (24.5) 47.9 Depreciation, depletion and amortization 14.8 8.1 1.6 24.5 Total assets (as of end of period) 924.1 472.7 387.9 1,784.7 Six Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Sales to external customers $ 584.7 $ 99.8 $ 21.2 $ 705.7 Intersegment sales — 3.8 (3.8) — Shipping and handling cost 187.7 13.6 0.6 201.9 Operating earnings (loss) (b)(c)(d) 116.9 (55.7) (162.3) (101.1) Depreciation, depletion and amortization 31.4 17.1 3.8 52.3 Six Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Sales to external customers $ 668.6 $ 89.3 $ 5.6 $ 763.5 Intersegment sales — 4.3 (4.3) — Shipping and handling cost 226.7 10.8 — 237.5 Operating earnings (loss) (c)(d) 120.2 10.3 (54.7) 75.8 Depreciation, depletion and amortization 28.7 16.4 3.3 48.4 Disaggregated revenue by product type is as follows (in millions): Three Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 227.6 $ — $ — $ 227.6 Consumer & Industrial Salt 82.8 — — 82.8 SOP — 50.8 — 50.8 Fire Retardant — — 0.1 0.1 Eliminations & Other — (0.7) 3.4 2.7 Sales to external customers $ 310.4 $ 50.1 $ 3.5 $ 364.0 Three Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 273.7 $ — $ — $ 273.7 Consumer & Industrial Salt 86.8 — — 86.8 SOP — 49.1 — 49.1 Eliminations & Other — (1.4) 2.9 1.5 Sales to external customers $ 360.5 $ 47.7 $ 2.9 $ 411.1 Six Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 387.0 $ — $ — $ 387.0 Consumer & Industrial Salt 197.7 — — 197.7 SOP — 103.6 — 103.6 Fire Retardant — — 14.1 14.1 Revenue from Services — — 0.5 0.5 Eliminations & Other — (3.8) 6.6 2.8 Sales to external customers $ 584.7 $ 99.8 $ 21.2 $ 705.7 Six Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 464.0 $ — $ — $ 464.0 Consumer & Industrial Salt 204.6 — — 204.6 SOP — 93.6 — 93.6 Eliminations & Other — (4.3) 5.6 1.3 Sales to external customers $ 668.6 $ 89.3 $ 5.6 $ 763.5 (a) Corporate and Other includes corporate entities, records management operations, the Fortress fire retardant business, equity method investments, 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, lithium-related expenses, as well as costs for the human resources, information technology, legal and finance functions. (b) The Company recognized impairments of $108.1 million and $182.9 million for the three and six months ended March 31, 2024, respectively, which impacted operating results. Refer to Note 1 for additional information regarding the Plant Nutrition and Fortress impairments and Note 5 for additional information about the impairment of lithium development assets. (c) Corporate operating results were impacted by net gains of $24.3 million and $21.4 million related to the decline in the valuation of the Fortress contingent consideration for the three and six months ended March 31, 2024, respectively. Corporate operating results also include net reimbursements related to the settled SEC investigation of $0.4 million and $0.1 million for the three and six months ended March 31, 2023, respectively. Refer to Note 9 for more information regarding the SEC investigation and settlement and Note 13 for information regarding the Fortress contingent consideration. (d) The Company continued to take steps to align its cost structure to its current business needs. These initiatives impacted Corporate operating results and resulted in net severance and related charges for reductions in workforce and changes to executive leadership and additional restructuring costs related to the termination of the Company’s lithium development project of $3.1 million and $5.6 million for the three and six months ended March 31, 2024, respectively, and $3.3 million for the three and six months ended March 31, 2023. The Company’s revenue by geographic area is as follows (in millions): Three Months Ended Six Months Ended Revenue 2024 2023 2024 2023 United States (a) $ 270.1 $ 283.1 $ 521.0 $ 531.3 Canada 78.1 101.0 155.7 188.6 United Kingdom 14.1 23.2 27.1 37.3 Other 1.7 3.8 1.9 6.3 Total revenue $ 364.0 $ 411.1 $ 705.7 $ 763.5 (a) United States sales exclude product sold to foreign customers at U.S. ports.

Stockholders' Equity and Equity

Stockholders' Equity and Equity Instruments	6 Months Ended
	Mar. 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. 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 16 – Stockholder’s Equity and Equity Instruments” within Part II, Item 8 of its 2023 Form 10-K. During the six months ended March 31, 2024, the Company reissued the following number of shares from treasury stock: 224,986 shares related to the release of RSUs which vested and 34,904 shares issued for Board of Director compensation . In fiscal 2023, the Company issued 158,132 net shares from treasury stock. The Company withheld a total of 86,749 shares with a fair value of $1.9 million related to the vesting of RSUs during the six months ended March 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 $0.6 million from its equity compensation awards during the six months ended March 31, 2024. During the six months ended March 31, 2024 and 2023, the Company recorded $8.3 million and $14.1 million (includes $1.3 million and $0.4 million paid in cash), respectively, of compensation expense pursuant to its stock-based compensation plans. No amounts have been capitalized. PSUs During the six months ended March 31, 2024, the Company issued new PSUs based upon several operational performance measures (“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 free cash flow, cash unit costs, cash unit cost reduction, capital expenditures and safety measures during the performance period and may range from 0% to 300% for each measure. The following table summarizes stock-based compensation activity during the six months ended March 31, 2024: Stock Options RSUs PSUs (a) Number Weighted-average Number Weighted-average Number Weighted-average Outstanding at September 30, 2023 642,995 $ 59.46 393,240 $ 42.50 393,579 $ 71.37 Granted — — 513,828 26.01 272,244 24.89 Exercised (b) — — — — — — Released from restriction (b) — — (224,986) 41.05 — — Cancelled/expired (10,036) 61.43 (136,999) 33.01 (360,496) 57.54 Outstanding at March 31, 2024 632,959 $ 59.43 545,083 $ 29.94 305,327 $ 46.28 (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 March 31, 2024 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (3.2) $ (6.4) $ 1.7 $ (83.8) $ (91.7) Other comprehensive loss before reclassifications (b) (0.2) — — (12.7) (12.9) Amounts reclassified from AOCL 0.8 0.2 — — 1.0 Net current period other comprehensive income (loss) 0.6 0.2 — (12.7) (11.9) Ending balance $ (2.6) $ (6.2) $ 1.7 $ (96.5) $ (103.6) Three Months Ended March 31, 2023 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (4.4) $ (2.6) $ 1.3 $ (100.6) $ (106.3) Other comprehensive (loss) income before reclassifications (b) (1.8) — — 2.8 1.0 Amounts reclassified from AOCL 0.7 — — — 0.7 Net current period other comprehensive (loss) income (1.1) — — 2.8 1.7 Ending balance $ (5.5) $ (2.6) $ 1.3 $ (97.8) $ (104.6) Six Months Ended March 31, 2024 (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 (loss) income before reclassifications (b) (2.8) — — 1.9 (0.9) Amounts reclassified from AOCL 1.6 0.4 — — 2.0 Net current period other comprehensive (loss) income (1.2) 0.4 — 1.9 1.1 Ending balance $ (2.6) $ (6.2) $ 1.7 $ (96.5) $ (103.6) Six Months Ended March 31, 2023 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (1.6) $ (2.7) $ 1.3 $ (112.3) $ (115.3) Other comprehensive (loss) income before reclassifications (b) (4.2) — — 14.5 10.3 Amounts reclassified from AOCL 0.3 0.1 — — 0.4 Net current period other comprehensive (loss) income (3.9) 0.1 — 14.5 10.7 Ending balance $ (5.5) $ (2.6) $ 1.3 $ (97.8) $ (104.6) (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 $2.3 million and $0.0 million in the three and six months ended March 31, 2024, respectively, and $(0.1) million and $(1.4) million in the three and six months ended March 31, 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 and six months ended March 31, 2024 and 2023, are shown below (in millions): Amount Reclassified from AOCL Three Months Ended Six Months Ended Line Item Impacted in the 2024 2023 2024 2023 Loss (gain) on cash flow hedges: Natural gas instruments $ 0.8 $ 1.0 $ 1.6 $ 0.5 Product cost Income tax expense — (0.3) — (0.2) Reclassifications, net of income taxes 0.8 0.7 1.6 0.3 Amortization of defined benefit pension: Amortization of loss 0.3 — 0.6 0.1 Product cost Income tax benefit (0.1) — (0.2) — Reclassifications, net of income taxes 0.2 — 0.4 0.1 Amortization of other post-employment benefits: Amortization of loss — — — — Product cost Income tax benefit — — — — Reclassifications, net of income taxes — — — — Total reclassifications, net of income taxes $ 1.0 $ 0.7 $ 2.0 $ 0.4

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Mar. 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 March 31, 2024 and September 30, 2023 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 March 31, 2024, the Company had entered into natural gas derivative instruments to hedge a portion of its natural gas purchase requirements through December 2025. As of March 31, 2024 and September 30, 2023, the Company had agreements in place to hedge forecasted natural gas purchases of 3.1 million a nd 2.3 million MMBtus, respectively. On March 1, 2023, the Company de-designated its natural gas cash flow hedges related to its Ogden, Utah production facility as the Company did not believe these hedges were probable of being highly effective in the second fiscal quarter of 2023. Beginning March 1, 2023, the change in the derivative was and will be recorded in other expense, net in the Consolidated Statements of Operations. Since the transactions are still probable of occurring, previously recognized amounts in AOCL of $0.3 million remain in AOCL until the underlying forecasted transaction occurs. The Company recognized $0.0 million and $0.7 million of expense in other expense, net on the Consolidated Statements of Operations during the three and six months ended March 31, 2024, respectively. Following the de-designation, these natural gas economic hedging instruments will be recorded at fair value through earnings unless re-designated or until settlement. Substantially all other natural gas derivative instruments held by the Company as of March 31, 2024 and September 30, 2023 qualified and were designated as cash flow hedges. As of March 31, 2024, the Company expects to reclassify from AOCL to earnings during the next twelve months $2.3 million of net losses on derivative instruments related to its natural gas hedges. Refer to Note 13 for the estimated fair value of the Company’s natural gas derivative instruments as of March 31, 2024 and September 30, 2023. The following tables present the fair value of the Company’s derivatives (in millions): Asset Derivatives Liability Derivatives Consolidated Balance Sheet Location March 31, 2024 Consolidated Balance Sheet Location March 31, 2024 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.9 Accrued expenses and other current liabilities $ 3.2 Commodity contracts Other assets 0.2 Other noncurrent liabilities 0.6 Total derivatives designated as hedging instruments 1.1 3.8 Derivatives not designated as hedging instruments: Commodity contracts Other current assets — Accrued expenses and other current liabilities 0.3 Total derivatives not designated as hedging instruments — 0.3 Total derivatives (a) $ 1.1 $ 4.1 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $1.1 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, 2023 Consolidated Balance Sheet Location September 30, 2023 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.9 Accrued expenses and other current liabilities $ 2.3 Total derivatives designated as hedging instruments 0.9 2.3 Derivatives not designated as hedging instruments: Commodity contracts Other current assets 0.1 Accrued expenses and other current liabilities — Total derivatives not designated as hedging instruments 0.1 — Total derivatives (a) $ 1.0 $ 2.3 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $1.0 million of its commodity contracts that are in receivable positions against its contracts in payable positions.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Mar. 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 and in Note 2 . 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 12 ). 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): March 31, Level One Level Two Level Three Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 3.0 $ 3.0 $ — $ — Total Assets $ 3.0 $ 3.0 $ — $ — Liability Class: Derivatives designated as hedging instruments - natural gas instruments, net $ (2.7) $ — $ (2.7) $ — Derivatives not designated as hedging instruments - natural gas instruments, net (0.3) — (0.3) — Liabilities related to non-qualified savings plan (3.0) (3.0) — — Total Liabilities $ (6.0) $ (3.0) $ (3.0) $ — (a) Includes mutual fund investments of approximately 30% in common stock of large-cap U.S. companies, 5% in common stock of small to mid-cap U.S. companies, 5% in international companies, 15% in bond funds, 5% in short-term investments and 40% in blended funds. September 30, Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 2.6 $ 2.6 $ — $ — Derivatives not designated as hedging instruments - natural gas instruments, net 0.1 — 0.1 — Total Assets $ 2.7 $ 2.6 $ 0.1 $ — Liability Class: Derivatives designated as hedging instruments - natural gas instruments, net $ (1.4) $ — $ (1.4) $ — Liabilities related to non-qualified savings plan (2.6) (2.6) — — Total Liabilities $ (4.0) $ (2.6) $ (1.4) $ — (a) Includes mutual fund investments of approximately 25% in the common stock of large-cap U.S. companies, 5% in the common stock of small to mid-cap U.S. companies, 10% in the common stock of international companies, 10% in bond funds, 5% in short-term investments and 45% 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 $3.0 million at March 31, 2024 and $2.6 million at September 30, 2023, are stated at fair value based on quoted market prices. As of March 31, 2024 and September 30, 2023, 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 $481.9 million and $472.5 million, respectively, compared with the aggregate principal amount at maturity of $500.0 million. The fair value at March 31, 2024 and September 30, 2023 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 $314.7 million and $277.1 million, respectively, compared with the aggregate principal amount at maturity of $318.5 million and $280.3 million, respectively. In connection with the acquisition of Fortress, the Company entered into a contingent consideration arrangement (milestone and earnout payments). 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 and six months ended March 31, 2024, the Company recorded income of $24.3 million and $21.4 million, respectively. The change in the second quarter of fiscal 2024 is reflective of milestone and earn-out payments made related to calendar year 2023 activity and recent developments related to the Company’s magnesium chloride-based fire retardants, as discussed further in Note 1 . The change is recorded in other operating (income) expense in the Consolidated Statement of Operations to reflect the contingent consideration liability at its fair value as of March 31, 2024. 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. Refer to Note 2 for a discussion of the milestone and earnout payments. The following table presents the fair value of the Company’s total contingent consideration arrangement (in millions): Consolidated Balance Sheet Location March 31, 2024 September 30, 2023 Accrued expenses and other current liabilities $ — $ 8.4 Other noncurrent liabilities 13.2 35.3 Total contingent consideration $ 13.2 $ 43.7 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 1 for details of the Company’s impairment of goodwill related to Plant Nutrition and Fortress, Note 5 for details of the Company’s impairment of long-lived assets related the termination of its lithium development and Note 6 for details of the Company’s intangible asset impairment related to Fortress.

Earnings per Share

Earnings per Share	6 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share: The Company calculates earnings per share using the two-class method. The two-class method requires allocating the Company’s net earnings to both common shares and participating securities. 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 Six Months Ended 2024 2023 2024 2023 Numerator: Net loss from continuing operations $ (48.0) $ (21.6) $ (123.1) $ (21.9) Less: net earnings allocated to participating securities (a) (0.1) (0.1) (0.2) (0.2) Net loss available to common stockholders $ (48.1) $ (21.7) $ (123.3) $ (22.1) Denominator (in thousands): Weighted-average common shares outstanding, shares for basic earnings per share 41,306 41,110 41,255 40,423 Weighted-average awards outstanding (b) — — — — Shares for diluted earnings per share 41,306 41,110 41,255 40,423 Basic net loss per common share $ (1.16) $ (0.53) $ (2.99) $ (0.55) Diluted net loss per common share $ (1.16) $ (0.53) $ (2.99) $ (0.55) (a) Weighted participating securities include RSUs and PSUs that receive non-forfeitable dividends and consist of 684,000 and 732,000 weighted participating securities for the three and six months ended March 31, 2024, respectively, and 439,000 and 477,000 weighted participating securities for the three and six months ended March 31, 2023, respectively. (b)

Related Party Transactions

Related Party Transactions	6 Months Ended
	Mar. 31, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions: During the three and six months ended March 31, 2024, the Company recorded SOP sales of approximately $1.0 million and $1.8 million, respectively, to certain subsidiaries of Koch Industries, Inc., compared to $0.9 million and $1.8 million, respectively, during the three and six months ended March 31, 2023. As of March 31, 2024 and September 30, 2023, the Company had approximately $0.5 million and $0.4 million, respectively, of receivables from related parties on its Consolidated Balance Sheets. There were no amounts payable outstanding as of March 31, 2024. On December 20, 2023 and March 20, 2024, the Company paid a cash dividend to its stockholders of record at the close of business on December 11, 2023 and March 11, 2024, respectively, in the amount of $0.15 per share. Koch Minerals & Trading,

Revision of Previously Issued F

Revision of Previously Issued Financial Statements	6 Months Ended
	Mar. 31, 2024
Accounting Changes and Error Corrections [Abstract]
Revision of Previously Issued Financial Statements	Revision of Previously Issued Financial Statements: As disclosed in Note 1 , the Company identified certain misstatements in the historical presentation of its Consolidated Statements of Cash Flows. The misstatements were the result of the Company not reflecting the appropriate amount of non-cash capital expenditures in accounts payable in its operating and investing cash flows and had no effect on the Company’s Consolidated Balance Sheets or its Consolidated Statements of Operations. Management has considered the misstatements, and after evaluating both their quantitative and qualitative impacts, concluded they are not material to the Company’s previously issued consolidated financial statements. The following tables show the cash flow classifications as reported and as corrected for the interim period ended March 31, 2023 and the interim period ended December 31, 2023. Three Months Ended December 31, 2023 (in millions) As Previously Reported Adjustments As Revised Cash flows from operating activities: Changes in operating assets and liabilities: Accounts payable and accrued expenses and other current liabilities $ (80.2) $ 13.6 $ (66.6) Net cash used in operating activities (65.6) 13.6 (52.0) Cash flows from investing activities: Capital expenditures (35.3) (13.6) (48.9) Net cash used in investing activities $ (36.0) $ (13.6) $ (49.6) Six Months Ended March 31, 2023 (in millions) As Previously Reported Adjustments As Revised Cash flows from operating activities: Changes in operating assets and liabilities: Accounts payable and accrued expenses and other current liabilities $ 35.6 $ 5.6 $ 41.2 Net cash provided by operating activities 143.9 5.6 149.5 Cash flows from investing activities: Capital expenditures (43.7) (5.6) (49.3) Net cash used in investing activities $ (44.0) $ (5.6) $ (49.6)

Subsequent Events

Subsequent Events	6 Months Ended
	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events: Dividend 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 payment of any future dividends will be at the discretion of the Board of Directors and will depend on the Company’s financial condition, results of operations, capital requirements, and any other factors deemed relevant by the Board of Directors.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net earnings (loss)	$ (48)	$ (21.6)	$ (123.1)	$ (21.9)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 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)	6 Months Ended
	Mar. 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, 2023, as filed with the Securities and Exchange Commission (the “SEC”) in its Annual Report on Form 10-K on November 29, 2023 (“2023 Form 10-K”). Certain amounts in prior periods have been reclassified to conform to the current period presentation. In the opinion of management, all adjustments, consisting of normal recurring adjustments considered necessary for a fair presentation, have been included.
Significant and Recent Accounting Pronouncements	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 2023 Form 10-K. There were no material changes in the Company’s significant accounting policies from those described in its 2023 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.
Revenues	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 March 31, 2024 and September 30, 2023 were not material.
Earnings per Share	The Company calculates earnings per share using the two-class method. The two-class method requires allocating the Company’s net earnings to both common shares and participating securities.

Accounting Policies and Basis_3

Accounting Policies and Basis of Presentation (Tables)	6 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Schedule of Impairments Incurred	A summary of the impairments incurred for the three and six months ended March 31, 2024, is detailed below (in millions): Impairment Financial Statement Line Item Segment Three Months Ended Six Months Ended Lithium long-lived assets, net Loss on impairments Corporate & Other $ — $ 74.8 Plant Nutrition goodwill Loss on impairments Plant Nutrition 51.0 51.0 Fortress goodwill Loss on impairments Corporate & Other 40.0 40.0 Fortress long-lived assets, net Loss on impairments Corporate & Other 15.6 15.6 Fortress inventory Product cost Corporate & Other 1.5 1.5 Total $ 108.1 $ 182.9

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Mar. 31, 2024
Inventory Disclosure [Abstract]
Schedule of Inventories	Inventories consist of the following (in millions): March 31, September 30, Finished goods $ 278.6 $ 319.3 Raw materials and supplies 89.1 72.9 Total inventories $ 367.7 $ 392.2

Property, Plant and Equipment_2

Property, Plant and Equipment, Net (Tables)	6 Months Ended
	Mar. 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): March 31, September 30, Land, buildings and structures, and leasehold improvements $ 550.4 $ 547.9 Machinery and equipment 1,131.4 1,102.0 Office furniture and equipment 22.3 21.6 Mineral interests 169.6 169.1 Construction in progress 60.2 113.0 1,933.9 1,953.6 Less: accumulated depreciation and depletion (1,140.4) (1,101.4) Property, plant and equipment, net $ 793.5 $ 852.2

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	6 Months Ended
	Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Changes in the carrying amount of goodwill are summarized as follows (in millions): Plant Nutrition Corporate & Other Consolidated Balance as of September 30, 2023 $ 51.1 $ 45.7 $ 96.8 Foreign currency translation adjustment 0.2 0.2 0.4 Balance as of December 31, 2023 $ 51.3 $ 45.9 $ 97.2 Foreign currency translation adjustment (0.3) — (0.3) Impairments (51.0) (40.0) (91.0) Balance as of March 31, 2024 $ — $ 5.9 $ 5.9

Long-Term Debt (Tables)

Long-Term Debt (Tables)	6 Months Ended
	Mar. 31, 2024
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-term debt consists of the following (in millions): March 31, September 30, 6.75% Senior Notes due December 2027 $ 500.0 $ 500.0 Term Loan due May 2028 196.3 198.8 Revolving Credit Facility due May 2028 122.2 81.5 AR Securitization Facility expires March 2027 64.8 30.9 883.3 811.2 Less unamortized debt issuance costs (6.1) (5.9) Total debt 877.2 805.3 Less current portion (5.0) (5.0) Long-term debt $ 872.2 $ 800.3

Operating Segments (Tables)

Operating Segments (Tables)	6 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Schedule of Segment Information	Segment information is as follows (in millions): Three Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Sales to external customers $ 310.4 $ 50.1 $ 3.5 $ 364.0 Intersegment sales — 0.7 (0.7) — Shipping and handling cost 104.0 6.6 — 110.6 Operating earnings (loss) (b)(c)(d) 66.4 (53.4) (58.8) (45.8) Depreciation, depletion and amortization 16.2 8.7 1.9 26.8 Total assets (as of end of period) 998.4 416.0 237.7 1,652.1 Three Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Sales to external customers $ 360.5 $ 47.7 $ 2.9 $ 411.1 Intersegment sales — 1.4 (1.4) — Shipping and handling cost 124.0 6.1 — 130.1 Operating earnings (loss) (c)(d) 73.1 (0.7) (24.5) 47.9 Depreciation, depletion and amortization 14.8 8.1 1.6 24.5 Total assets (as of end of period) 924.1 472.7 387.9 1,784.7 Six Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Sales to external customers $ 584.7 $ 99.8 $ 21.2 $ 705.7 Intersegment sales — 3.8 (3.8) — Shipping and handling cost 187.7 13.6 0.6 201.9 Operating earnings (loss) (b)(c)(d) 116.9 (55.7) (162.3) (101.1) Depreciation, depletion and amortization 31.4 17.1 3.8 52.3 Six Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Sales to external customers $ 668.6 $ 89.3 $ 5.6 $ 763.5 Intersegment sales — 4.3 (4.3) — Shipping and handling cost 226.7 10.8 — 237.5 Operating earnings (loss) (c)(d) 120.2 10.3 (54.7) 75.8 Depreciation, depletion and amortization 28.7 16.4 3.3 48.4
Schedule of Disaggregated Revenue by Product Type	Disaggregated revenue by product type is as follows (in millions): Three Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 227.6 $ — $ — $ 227.6 Consumer & Industrial Salt 82.8 — — 82.8 SOP — 50.8 — 50.8 Fire Retardant — — 0.1 0.1 Eliminations & Other — (0.7) 3.4 2.7 Sales to external customers $ 310.4 $ 50.1 $ 3.5 $ 364.0 Three Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 273.7 $ — $ — $ 273.7 Consumer & Industrial Salt 86.8 — — 86.8 SOP — 49.1 — 49.1 Eliminations & Other — (1.4) 2.9 1.5 Sales to external customers $ 360.5 $ 47.7 $ 2.9 $ 411.1 Six Months Ended March 31, 2024 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 387.0 $ — $ — $ 387.0 Consumer & Industrial Salt 197.7 — — 197.7 SOP — 103.6 — 103.6 Fire Retardant — — 14.1 14.1 Revenue from Services — — 0.5 0.5 Eliminations & Other — (3.8) 6.6 2.8 Sales to external customers $ 584.7 $ 99.8 $ 21.2 $ 705.7 Six Months Ended March 31, 2023 Salt Plant Corporate & Other (a) Total Highway Deicing Salt $ 464.0 $ — $ — $ 464.0 Consumer & Industrial Salt 204.6 — — 204.6 SOP — 93.6 — 93.6 Eliminations & Other — (4.3) 5.6 1.3 Sales to external customers $ 668.6 $ 89.3 $ 5.6 $ 763.5 (a) Corporate and Other includes corporate entities, records management operations, the Fortress fire retardant business, equity method investments, 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, lithium-related expenses, as well as costs for the human resources, information technology, legal and finance functions. (b) The Company recognized impairments of $108.1 million and $182.9 million for the three and six months ended March 31, 2024, respectively, which impacted operating results. Refer to Note 1 for additional information regarding the Plant Nutrition and Fortress impairments and Note 5 for additional information about the impairment of lithium development assets. (c) Corporate operating results were impacted by net gains of $24.3 million and $21.4 million related to the decline in the valuation of the Fortress contingent consideration for the three and six months ended March 31, 2024, respectively. Corporate operating results also include net reimbursements related to the settled SEC investigation of $0.4 million and $0.1 million for the three and six months ended March 31, 2023, respectively. Refer to Note 9 for more information regarding the SEC investigation and settlement and Note 13 for information regarding the Fortress contingent consideration. (d) The Company continued to take steps to align its cost structure to its current business needs. These initiatives impacted Corporate operating results and resulted in net severance and related charges for reductions in workforce and changes to executive leadership and additional restructuring costs related to the termination of the Company’s lithium development project of $3.1 million and $5.6 million for the three and six months ended March 31, 2024, respectively, and $3.3 million for the three and six months ended March 31, 2023.
Schedule of Revenue by Geographic Area	The Company’s revenue by geographic area is as follows (in millions): Three Months Ended Six Months Ended Revenue 2024 2023 2024 2023 United States (a) $ 270.1 $ 283.1 $ 521.0 $ 531.3 Canada 78.1 101.0 155.7 188.6 United Kingdom 14.1 23.2 27.1 37.3 Other 1.7 3.8 1.9 6.3 Total revenue $ 364.0 $ 411.1 $ 705.7 $ 763.5 (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)	6 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Schedule of Stock-Based Compensation Activity	The following table summarizes stock-based compensation activity during the six months ended March 31, 2024: Stock Options RSUs PSUs (a) Number Weighted-average Number Weighted-average Number Weighted-average Outstanding at September 30, 2023 642,995 $ 59.46 393,240 $ 42.50 393,579 $ 71.37 Granted — — 513,828 26.01 272,244 24.89 Exercised (b) — — — — — — Released from restriction (b) — — (224,986) 41.05 — — Cancelled/expired (10,036) 61.43 (136,999) 33.01 (360,496) 57.54 Outstanding at March 31, 2024 632,959 $ 59.43 545,083 $ 29.94 305,327 $ 46.28 (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 March 31, 2024 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (3.2) $ (6.4) $ 1.7 $ (83.8) $ (91.7) Other comprehensive loss before reclassifications (b) (0.2) — — (12.7) (12.9) Amounts reclassified from AOCL 0.8 0.2 — — 1.0 Net current period other comprehensive income (loss) 0.6 0.2 — (12.7) (11.9) Ending balance $ (2.6) $ (6.2) $ 1.7 $ (96.5) $ (103.6) Three Months Ended March 31, 2023 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (4.4) $ (2.6) $ 1.3 $ (100.6) $ (106.3) Other comprehensive (loss) income before reclassifications (b) (1.8) — — 2.8 1.0 Amounts reclassified from AOCL 0.7 — — — 0.7 Net current period other comprehensive (loss) income (1.1) — — 2.8 1.7 Ending balance $ (5.5) $ (2.6) $ 1.3 $ (97.8) $ (104.6) Six Months Ended March 31, 2024 (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 (loss) income before reclassifications (b) (2.8) — — 1.9 (0.9) Amounts reclassified from AOCL 1.6 0.4 — — 2.0 Net current period other comprehensive (loss) income (1.2) 0.4 — 1.9 1.1 Ending balance $ (2.6) $ (6.2) $ 1.7 $ (96.5) $ (103.6) Six Months Ended March 31, 2023 (a) Gains and (Losses) on Cash Flow Hedges Defined Benefit Pension Other Post-Employment Benefits Foreign Currency Total Beginning balance $ (1.6) $ (2.7) $ 1.3 $ (112.3) $ (115.3) Other comprehensive (loss) income before reclassifications (b) (4.2) — — 14.5 10.3 Amounts reclassified from AOCL 0.3 0.1 — — 0.4 Net current period other comprehensive (loss) income (3.9) 0.1 — 14.5 10.7 Ending balance $ (5.5) $ (2.6) $ 1.3 $ (97.8) $ (104.6) (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 $2.3 million and $0.0 million in the three and six months ended March 31, 2024, respectively, and $(0.1) million and $(1.4) million in the three and six months ended March 31, 2023, respectively, in AOCL related to intercompany notes which were deemed to be of a long-term investment nature.
Schedule of Reclassifications out of Accumulated Other Comprehensive Income	The amounts reclassified from AOCL to expense (income) for the three and six months ended March 31, 2024 and 2023, are shown below (in millions): Amount Reclassified from AOCL Three Months Ended Six Months Ended Line Item Impacted in the 2024 2023 2024 2023 Loss (gain) on cash flow hedges: Natural gas instruments $ 0.8 $ 1.0 $ 1.6 $ 0.5 Product cost Income tax expense — (0.3) — (0.2) Reclassifications, net of income taxes 0.8 0.7 1.6 0.3 Amortization of defined benefit pension: Amortization of loss 0.3 — 0.6 0.1 Product cost Income tax benefit (0.1) — (0.2) — Reclassifications, net of income taxes 0.2 — 0.4 0.1 Amortization of other post-employment benefits: Amortization of loss — — — — Product cost Income tax benefit — — — — Reclassifications, net of income taxes — — — — Total reclassifications, net of income taxes $ 1.0 $ 0.7 $ 2.0 $ 0.4

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	6 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Fair Value of Hedges	The following tables present the fair value of the Company’s derivatives (in millions): Asset Derivatives Liability Derivatives Consolidated Balance Sheet Location March 31, 2024 Consolidated Balance Sheet Location March 31, 2024 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.9 Accrued expenses and other current liabilities $ 3.2 Commodity contracts Other assets 0.2 Other noncurrent liabilities 0.6 Total derivatives designated as hedging instruments 1.1 3.8 Derivatives not designated as hedging instruments: Commodity contracts Other current assets — Accrued expenses and other current liabilities 0.3 Total derivatives not designated as hedging instruments — 0.3 Total derivatives (a) $ 1.1 $ 4.1 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $1.1 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, 2023 Consolidated Balance Sheet Location September 30, 2023 Derivatives designated as hedging instruments: Commodity contracts Other current assets $ 0.9 Accrued expenses and other current liabilities $ 2.3 Total derivatives designated as hedging instruments 0.9 2.3 Derivatives not designated as hedging instruments: Commodity contracts Other current assets 0.1 Accrued expenses and other current liabilities — Total derivatives not designated as hedging instruments 0.1 — Total derivatives (a) $ 1.0 $ 2.3 (a) The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $1.0 million of its commodity contracts that are in receivable positions against its contracts in payable positions.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The estimated fair values for each type of instrument are presented below (in millions): March 31, Level One Level Two Level Three Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 3.0 $ 3.0 $ — $ — Total Assets $ 3.0 $ 3.0 $ — $ — Liability Class: Derivatives designated as hedging instruments - natural gas instruments, net $ (2.7) $ — $ (2.7) $ — Derivatives not designated as hedging instruments - natural gas instruments, net (0.3) — (0.3) — Liabilities related to non-qualified savings plan (3.0) (3.0) — — Total Liabilities $ (6.0) $ (3.0) $ (3.0) $ — (a) Includes mutual fund investments of approximately 30% in common stock of large-cap U.S. companies, 5% in common stock of small to mid-cap U.S. companies, 5% in international companies, 15% in bond funds, 5% in short-term investments and 40% in blended funds. September 30, Asset Class: Mutual fund investments in a non-qualified savings plan (a) $ 2.6 $ 2.6 $ — $ — Derivatives not designated as hedging instruments - natural gas instruments, net 0.1 — 0.1 — Total Assets $ 2.7 $ 2.6 $ 0.1 $ — Liability Class: Derivatives designated as hedging instruments - natural gas instruments, net $ (1.4) $ — $ (1.4) $ — Liabilities related to non-qualified savings plan (2.6) (2.6) — — Total Liabilities $ (4.0) $ (2.6) $ (1.4) $ — (a) Includes mutual fund investments of approximately 25% in the common stock of large-cap U.S. companies, 5% in the common stock of small to mid-cap U.S. companies, 10% in the common stock of international companies, 10% in bond funds, 5% in short-term investments and 45% in blended funds.
Schedule of Business Acquisitions by Acquisition, Contingent Consideration	The following table presents the fair value of the Company’s total contingent consideration arrangement (in millions): Consolidated Balance Sheet Location March 31, 2024 September 30, 2023 Accrued expenses and other current liabilities $ — $ 8.4 Other noncurrent liabilities 13.2 35.3 Total contingent consideration $ 13.2 $ 43.7

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Schedule 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 Six Months Ended 2024 2023 2024 2023 Numerator: Net loss from continuing operations $ (48.0) $ (21.6) $ (123.1) $ (21.9) Less: net earnings allocated to participating securities (a) (0.1) (0.1) (0.2) (0.2) Net loss available to common stockholders $ (48.1) $ (21.7) $ (123.3) $ (22.1) Denominator (in thousands): Weighted-average common shares outstanding, shares for basic earnings per share 41,306 41,110 41,255 40,423 Weighted-average awards outstanding (b) — — — — Shares for diluted earnings per share 41,306 41,110 41,255 40,423 Basic net loss per common share $ (1.16) $ (0.53) $ (2.99) $ (0.55) Diluted net loss per common share $ (1.16) $ (0.53) $ (2.99) $ (0.55) (a) Weighted participating securities include RSUs and PSUs that receive non-forfeitable dividends and consist of 684,000 and 732,000 weighted participating securities for the three and six months ended March 31, 2024, respectively, and 439,000 and 477,000 weighted participating securities for the three and six months ended March 31, 2023, respectively. (b)

Revision of Previously Issued_2

Revision of Previously Issued Financial Statements (Tables)	6 Months Ended
	Mar. 31, 2024
Accounting Changes and Error Corrections [Abstract]
Schedule of Cash Flow Classifications	The following tables show the cash flow classifications as reported and as corrected for the interim period ended March 31, 2023 and the interim period ended December 31, 2023. Three Months Ended December 31, 2023 (in millions) As Previously Reported Adjustments As Revised Cash flows from operating activities: Changes in operating assets and liabilities: Accounts payable and accrued expenses and other current liabilities $ (80.2) $ 13.6 $ (66.6) Net cash used in operating activities (65.6) 13.6 (52.0) Cash flows from investing activities: Capital expenditures (35.3) (13.6) (48.9) Net cash used in investing activities $ (36.0) $ (13.6) $ (49.6) Six Months Ended March 31, 2023 (in millions) As Previously Reported Adjustments As Revised Cash flows from operating activities: Changes in operating assets and liabilities: Accounts payable and accrued expenses and other current liabilities $ 35.6 $ 5.6 $ 41.2 Net cash provided by operating activities 143.9 5.6 149.5 Cash flows from investing activities: Capital expenditures (43.7) (5.6) (49.3) Net cash used in investing activities $ (44.0) $ (5.6) $ (49.6)

Accounting Policies and Basis_4

Accounting Policies and Basis of Presentation - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2024
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, loss on impairment	$ 91	$ 91
Corporate & Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, loss on impairment	40	40
Developed technology
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impairment of intangible asset	15.6
Plant Nutrition
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, loss on impairment	51	51
Finished goods inventory
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impairment of finished goods	$ 1.5	$ 1.5

Accounting Policies and Basis_5

Accounting Policies and Basis of Presentation - Schedule of Impairments Incurred (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2024
Impaired Long-Lived Assets Held and Used [Line Items]
Loss on impairments	$ 108.1	$ 182.9
Corporate & Other | Lithium long-lived assets, net
Impaired Long-Lived Assets Held and Used [Line Items]
Loss on impairments	0	74.8
Corporate & Other | Fortress goodwill
Impaired Long-Lived Assets Held and Used [Line Items]
Loss on impairments	40	40
Corporate & Other | Fortress long-lived assets, net
Impaired Long-Lived Assets Held and Used [Line Items]
Loss on impairments	15.6	15.6
Corporate & Other | Fortress inventory
Impaired Long-Lived Assets Held and Used [Line Items]
Loss on impairments	1.5	1.5
Plant Nutrition | Plant Nutrition goodwill
Impaired Long-Lived Assets Held and Used [Line Items]
Loss on impairments	$ 51	$ 51

Business Acquisition - Narrativ

Business Acquisition - Narrative (Details) - USD ($) $ in Millions	May 05, 2023	Mar. 31, 2024	Sep. 30, 2023
Business Acquisition [Line Items]
Contingent consideration, liability		$ 13.2	$ 43.7
Fortress
Business Acquisition [Line Items]
Ownership interest in investment	45%
Fortress
Business Acquisition [Line Items]
Remaining interest acquired (as a percent)	55%
Acquisition of business, net of cash acquired	$ 18.9
Cash held by acquiree	6.5
Contingent consideration, liability	$ 28
Performance period	5 years
Contingent consideration period	10 years

Revenues (Details)

Revenues (Details) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Deferred revenue	$ 4.1	$ 8.5

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023
Inventory Disclosure [Abstract]
Finished goods	$ 278.6	$ 319.3
Raw materials and supplies	89.1	72.9
Total inventories	$ 367.7	$ 392.2

Property, Plant and Equipment_3

Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2024	Sep. 30, 2023
Property, Plant and Equipment [Line Items]
Total property plant and equipment	$ 1,933.9	$ 1,933.9	$ 1,953.6
Less: accumulated depreciation and depletion	(1,140.4)	(1,140.4)	(1,101.4)
Property, plant and equipment, net	793.5	793.5	852.2
Loss on impairments	108.1	182.9
Loss on impairment of long-lived assets, future commitments	5.9	5.9
Corporate & Other | Lithium long-lived assets, net
Property, Plant and Equipment [Line Items]
Loss on impairments	0	74.8
Land, buildings and structures, and leasehold improvements
Property, Plant and Equipment [Line Items]
Total property plant and equipment	550.4	550.4	547.9
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property plant and equipment	1,131.4	1,131.4	1,102
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Total property plant and equipment	22.3	22.3	21.6
Mineral interests
Property, Plant and Equipment [Line Items]
Total property plant and equipment	169.6	169.6	169.1
Construction in progress
Property, Plant and Equipment [Line Items]
Total property plant and equipment	60.2	60.2	$ 113
Lithium Salt Resource
Property, Plant and Equipment [Line Items]
Property, plant and equipment	72.7	72.7
Property, plant and equipment remaining	$ 5.1	$ 5.1

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2024
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 97.2	$ 96.8	$ 96.8
Foreign currency translation adjustment	(0.3)	0.4
Impairments	(91)		(91)
Goodwill, ending balance	5.9	97.2	5.9
Corporate & Other
Goodwill [Roll Forward]
Goodwill, beginning balance	45.9	45.7	45.7
Foreign currency translation adjustment	0	0.2
Impairments	(40)		(40)
Goodwill, ending balance	5.9	45.9	5.9
Plant Nutrition
Goodwill [Roll Forward]
Goodwill, beginning balance	51.3	51.1	51.1
Foreign currency translation adjustment	(0.3)	0.2
Impairments	(51)		(51)
Goodwill, ending balance	$ 0	$ 51.3	$ 0

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Indefinite-lived in-process research and development
Indefinite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 2.2
Developed technology
Indefinite-Lived Intangible Assets [Line Items]
Impairment of intangible asset	15.6
Accumulated amortization	0.4
Customer relationships
Indefinite-Lived Intangible Assets [Line Items]
Net intangible assets	55.2
Trade names
Indefinite-Lived Intangible Assets [Line Items]
Net intangible assets	$ 0.2

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2024	Sep. 30, 2023
Income Tax Disclosure [Line Items]
Nondeductible executive compensation	$ 1
U.S. Federal
Income Tax Disclosure [Line Items]
Deferred tax asset valuation allowance recorded	28.3
Foreign Tax Authority
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	65.5	$ 65.4
Foreign Tax Authority | Canadian Tax Authority
Income Tax Disclosure [Line Items]
Total reassessments including interest	188.7
Amount of security posted in the form of a performance bond	161.9
Amount of security posted in the form of cash	36.7	36.7
State and Local | NOL carryforwards expire beginning in 2035
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 2.9	$ 2.9

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Long-term debt, gross	$ 883.3	$ 811.2
Less unamortized debt issuance costs	(6.1)	(5.9)
Total debt	877.2	805.3
Less current portion	(5)	(5)
Long-term debt	$ 872.2	$ 800.3
Senior Notes | 6.75% Senior Notes due December 2027
Debt Instrument [Line Items]
Stated interest rate (as a percent)	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	196.3	198.8
Line of Credit | Revolving Credit Facility due May 2028
Debt Instrument [Line Items]
Long-term debt, gross	122.2	81.5
Line of Credit | AR Securitization Facility expires March 2027
Debt Instrument [Line Items]
Long-term debt, gross	$ 64.8	$ 30.9

Long-Term Debt - Narrative (Det

Long-Term Debt - Narrative (Details) $ in Millions	6 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 27, 2024 USD ($)	Sep. 30, 2023
Account Receivable Financing Receivable
Debt Instrument [Line Items]
Fees paid for extension		$ 0.4
Line of Credit | 2023 Credit Agreement
Debt Instrument [Line Items]
Deferred financing costs		$ 1.7
Additional legal fees	$ 0.9
Line of Credit | 2023 Credit Agreement | Fiscal quarter ended March 31, 2024
Debt Instrument [Line Items]
Consolidated total net leverage ratio		6
Line of Credit | 2023 Credit Agreement | Fiscal quarter ended December 31, 2024
Debt Instrument [Line Items]
Consolidated total net leverage ratio		6.5
Line of Credit | 2023 Credit Agreement | Fiscal quarter ended March 31, 2026 and thereafter
Debt Instrument [Line Items]
Consolidated total net leverage ratio		4.75
Line of Credit | Revolving Credit Facility Due January 2025
Debt Instrument [Line Items]
Weighted average interest rate of debt (as a percent)	8.40%		7.80%
Line of Credit | Revolving Credit Facility Due January 2025 | Minimum
Debt Instrument [Line Items]
Weighted average interest rate of debt (as a percent)	8.20%		7.70%
Line of Credit | Revolving Credit Facility Due January 2025 | Maximum
Debt Instrument [Line Items]
Weighted average interest rate of debt (as a percent)	10.30%		9.80%
Line of Credit | Revolving Credit Facility | 2023 Credit Agreement
Debt Instrument [Line Items]
Availability under revolving credit facility	$ 237.7
Aggregate principal amount of credit facility	375
Line of Credit | Revolving Credit Facility | Revolving Credit Facility Due January 2025
Debt Instrument [Line Items]
Maximum unrestricted cash	$ 75

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Apr. 24, 2024 officer	Sep. 23, 2022 USD ($)
SEC Investigation
Loss Contingencies [Line Items]
Loss contingency, damages sought, value | $		$ 12
Contingent loss accrual | $		$ 10
Class Action Lawsuit Filed In District Of Kansas | Former Officer | Pending Litigation | Subsequent Event
Loss Contingencies [Line Items]
Number of defendants | officer	1
Class Action Lawsuit Filed In District Of Kansas | Current Officer | Pending Litigation | Subsequent Event
Loss Contingencies [Line Items]
Number of defendants | officer	3

Operating Segments - Narrative

Operating Segments - Narrative (Details) - segment	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting [Abstract]
Number of reportable segments	2	2

Operating Segments (Details)

Operating Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($) segment
Segment Reporting [Abstract]
Number of reportable segments | segment	2			2
Segment Reporting Information [Abstract]
Sales	$ 364	$ 411.1	$ 705.7	$ 763.5
Operating earnings (loss)	(45.8)	47.9	(101.1)	75.8
Depreciation, depletion and amortization	26.8	24.5	52.3	48.4
Total assets (as of end of period)	1,652.1	1,784.7	1,652.1	1,784.7
Loss on impairments	108.1		182.9
Increase to contingent consideration liability			(21.4)	0
Accrued loss reserve		(0.4)		(0.1)
Severance costs	3.1		5.6
Restructuring charges	1.7	3.3		3.3
Fortress
Segment Reporting Information [Abstract]
Increase to contingent consideration liability	24.3		21.4
United States
Segment Reporting Information [Abstract]
Sales	270.1	283.1	521	531.3
Canada
Segment Reporting Information [Abstract]
Sales	78.1	101	155.7	188.6
United Kingdom
Segment Reporting Information [Abstract]
Sales	14.1	23.2	27.1	37.3
Other
Segment Reporting Information [Abstract]
Sales	1.7	3.8	1.9	6.3
Shipping and handling cost
Segment Reporting Information [Abstract]
Shipping and handling cost	110.6	130.1	201.9	237.5
Highway Deicing Salt
Segment Reporting Information [Abstract]
Sales	227.6	273.7	387	464
Consumer & Industrial Salt
Segment Reporting Information [Abstract]
Sales	82.8	86.8	197.7	204.6
SOP
Segment Reporting Information [Abstract]
Sales	50.8	49.1	103.6	93.6
Fire Retardant
Segment Reporting Information [Abstract]
Sales	0.1		14.1
Revenue from Services
Segment Reporting Information [Abstract]
Sales			0.5
Eliminations & Other
Segment Reporting Information [Abstract]
Sales	2.7	1.5
Operating Segments | Salt
Segment Reporting Information [Abstract]
Sales	310.4	360.5	584.7	668.6
Operating earnings (loss)	66.4	73.1	116.9	120.2
Depreciation, depletion and amortization	16.2	14.8	31.4	28.7
Total assets (as of end of period)	998.4	924.1	998.4	924.1
Operating Segments | Salt | Shipping and handling cost
Segment Reporting Information [Abstract]
Shipping and handling cost	104	124	187.7	226.7
Operating Segments | Salt | Highway Deicing Salt
Segment Reporting Information [Abstract]
Sales	227.6	273.7	387	464
Operating Segments | Salt | Consumer & Industrial Salt
Segment Reporting Information [Abstract]
Sales	82.8	86.8	197.7	204.6
Operating Segments | Salt | SOP
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Operating Segments | Salt | Fire Retardant
Segment Reporting Information [Abstract]
Sales	0		0
Operating Segments | Salt | Revenue from Services
Segment Reporting Information [Abstract]
Sales			0
Operating Segments | Salt | Eliminations & Other
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Operating Segments | Plant Nutrition
Segment Reporting Information [Abstract]
Sales	50.1	47.7	99.8	89.3
Operating earnings (loss)	(53.4)	(0.7)	(55.7)	10.3
Depreciation, depletion and amortization	8.7	8.1	17.1	16.4
Total assets (as of end of period)	416	472.7	416	472.7
Operating Segments | Plant Nutrition | Shipping and handling cost
Segment Reporting Information [Abstract]
Shipping and handling cost	6.6	6.1	13.6	10.8
Operating Segments | Plant Nutrition | Highway Deicing Salt
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Operating Segments | Plant Nutrition | Consumer & Industrial Salt
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Operating Segments | Plant Nutrition | SOP
Segment Reporting Information [Abstract]
Sales	50.8	49.1	103.6	93.6
Operating Segments | Plant Nutrition | Fire Retardant
Segment Reporting Information [Abstract]
Sales	0		0
Operating Segments | Plant Nutrition | Revenue from Services
Segment Reporting Information [Abstract]
Sales			0
Operating Segments | Plant Nutrition | Eliminations & Other
Segment Reporting Information [Abstract]
Sales	(0.7)	(1.4)	(3.8)	(4.3)
Corporate & Other
Segment Reporting Information [Abstract]
Sales	3.5	2.9	21.2	5.6
Operating earnings (loss)	(58.8)	(24.5)	(162.3)	(54.7)
Depreciation, depletion and amortization	1.9	1.6	3.8	3.3
Total assets (as of end of period)	237.7	387.9	237.7	387.9
Corporate & Other | Shipping and handling cost
Segment Reporting Information [Abstract]
Shipping and handling cost	0	0	0.6	0
Corporate & Other | Highway Deicing Salt
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Corporate & Other | Consumer & Industrial Salt
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Corporate & Other | SOP
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Corporate & Other | Fire Retardant
Segment Reporting Information [Abstract]
Sales	0.1		14.1
Corporate & Other | Revenue from Services
Segment Reporting Information [Abstract]
Sales			0.5
Corporate & Other | Eliminations & Other
Segment Reporting Information [Abstract]
Sales	3.4	2.9	6.6	5.6
Intersegment Eliminations
Segment Reporting Information [Abstract]
Sales	(0.7)	(1.4)	(3.8)	(4.3)
Intersegment Eliminations | Eliminations & Other
Segment Reporting Information [Abstract]
Sales			2.8	1.3
Intersegment Eliminations | Salt
Segment Reporting Information [Abstract]
Sales	0	0	0	0
Intersegment Eliminations | Plant Nutrition
Segment Reporting Information [Abstract]
Sales	$ 0.7	$ 1.4	$ 3.8	$ 4.3

Stockholders' Equity and Equi_3

Stockholders' Equity and Equity Instruments - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	6 Months Ended
	Feb. 28, 2022	Mar. 31, 2024	Mar. 31, 2023	May 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury stock reissued (in shares)		158,132
Tax deficiency from equity compensation awards recorded as an increase to income tax expense		$ 0.6
Share-based payment arrangement, expense		8.3	$ 14.1
Compensation expense to be paid in cash		$ 1.3	$ 0.4
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reissued share of treasury stock		224,986
Stock Payments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reissued share of treasury stock		34,904
Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld related to vesting of RSUs and PSUs (in shares)		86,749
Fair value of stock withheld related to vesting of RSUs and PSUs		$ 1.9
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		300%
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)	750,000

Stockholders' Equity and Equi_4

Stockholders' Equity and Equity Instruments - Schedule of Stock-Based Compensation Activity (Details)	6 Months Ended
	Mar. 31, 2024 $ / shares shares
Stock Options
Number
Outstanding at beginning of period (in shares)	642,995
Granted (in shares)	0
Exercised (in shares)	0
Released from restriction (in shares)	0
Cancelled/expired (in shares)	(10,036)
Outstanding at end of period (in shares)	632,959
Weighted-average exercise price
Weighted-average exercise price at beginning of period (in dollars per share) | $ / shares	$ 59.46
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	61.43
Weighted-average exercise price at end of period (in dollars per share) | $ / shares	$ 59.43
RSUs
Number
Outstanding at beginning of period (in shares)	393,240
Granted (in shares)	513,828
Exercised (in shares)	0
Released from restriction (in shares)	(224,986)
Cancelled/expired (in shares)	(136,999)
Outstanding at end of period (in shares)	545,083
Weighted-average fair value
Weighted-average fair value at beginning of period (in dollars per share) | $ / shares	$ 42.50
Weighted-average fair value, granted (in dollars per share) | $ / shares	26.01
Weighted-average fair value, exercised (in dollars per share) | $ / shares	0
Weighted-average fair value, released from restriction (in dollars per share) | $ / shares	41.05
Weighted-average fair value, cancelled/expired (in dollars per share) | $ / shares	33.01
Weighted-average fair value at end of period (in dollars per share) | $ / shares	$ 29.94
PSUs
Number
Outstanding at beginning of period (in shares)	393,579
Granted (in shares)	272,244
Exercised (in shares)	0
Released from restriction (in shares)	0
Cancelled/expired (in shares)	(360,496)
Outstanding at end of period (in shares)	305,327
Weighted-average fair value
Weighted-average fair value at beginning of period (in dollars per share) | $ / shares	$ 71.37
Weighted-average fair value, granted (in dollars per share) | $ / shares	24.89
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	57.54
Weighted-average fair value at end of period (in dollars per share) | $ / shares	$ 46.28
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 AOCL (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 459.8	$ 509.8	$ 517.2	$ 256.4
Other comprehensive (loss) income before reclassifications	(12.9)	1	(0.9)	10.3
Amounts reclassified from AOCL	1	0.7	2	0.4
Net current period other comprehensive (loss) income	(11.9)	1.7	1.1	10.7
Ending balance	387.7	485.4	387.7	485.4
Gain (loss) on foreign exchange of intercompany notes of long-term nature	2.3	(0.1)	0	(1.4)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(91.7)	(106.3)	(104.7)	(115.3)
Ending balance	(103.6)	(104.6)	(103.6)	(104.6)
Gains and (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(3.2)	(4.4)	(1.4)	(1.6)
Other comprehensive (loss) income before reclassifications	(0.2)	(1.8)	(2.8)	(4.2)
Amounts reclassified from AOCL	0.8	0.7	1.6	0.3
Net current period other comprehensive (loss) income	0.6	(1.1)	(1.2)	(3.9)
Ending balance	(2.6)	(5.5)	(2.6)	(5.5)
Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(2.6)		(2.7)
Other comprehensive (loss) income before reclassifications		0		0
Amounts reclassified from AOCL		0		0.1
Net current period other comprehensive (loss) income		0		0.1
Ending balance		(2.6)		(2.6)
Benefit Plans | Defined Benefit Pension
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(6.4)		(6.6)
Other comprehensive (loss) income before reclassifications	0		0
Amounts reclassified from AOCL	0.2		0.4
Net current period other comprehensive (loss) income	0.2		0.4
Ending balance	(6.2)		(6.2)
Benefit Plans | Other Post-Employment Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	1.7	1.3	1.7	1.3
Other comprehensive (loss) income before reclassifications	0	0	0	0
Amounts reclassified from AOCL	0	0	0	0
Net current period other comprehensive (loss) income	0	0	0	0
Ending balance	1.7	1.3	1.7	1.3
Foreign Currency
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(83.8)	(100.6)	(98.4)	(112.3)
Other comprehensive (loss) income before reclassifications	(12.7)	2.8	1.9	14.5
Amounts reclassified from AOCL	0	0	0	0
Net current period other comprehensive (loss) income	(12.7)	2.8	1.9	14.5
Ending balance	$ (96.5)	$ (97.8)	$ (96.5)	$ (97.8)

Stockholders' Equity and Equi_6

Stockholders' Equity and Equity Instruments - Schedule of Reclassifications From AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax benefit (expense)	$ (13.1)	$ 55.1	$ (11.3)	$ 67
Net earnings (loss)	(48)	(21.6)	(123.1)	(21.9)
Product cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Product cost	(180.5)	(195.8)	(360.3)	(370.8)
Amount Reclassified from AOCL
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net earnings (loss)	1	0.7	2	0.4
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	(0.3)	0	(0.2)
Net earnings (loss)	0.8	0.7	1.6	0.3
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	0.8	1	1.6	0.5
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	(0.2)	0
Net earnings (loss)	0.2	0	0.4	0.1
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	0.6	0.1
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	0	0
Net earnings (loss)	0	0	0	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	$ 0	$ 0	$ 0

Derivative Financial Instrume_3

Derivative Financial Instruments - Narrative (Details) MMBTU in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($) MMBTU	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($) MMBTU	Mar. 01, 2023 USD ($)
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 4.1		$ 4.1		$ 2.3
Expense recognized	(0.9)	$ (0.9)	(1.6)	$ (1)
Net gains to be reclassified from accumulated other comprehensive loss to earnings during the next 12 months			2.3
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Liability Derivatives	3.8		3.8		2.3
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Liability Derivatives	0.3		$ 0.3		$ 0
Natural gas instruments
Derivatives, Fair Value [Line Items]
Notional amount (in MMBtus) | MMBTU			3.1		2.3
Expense recognized	$ 0		$ 0.7
Natural gas instruments | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Percent of forecasted usage to be hedged	90%		90%
Maximum period which the company hedges in advance of forecasted purchase			36 months
Natural gas instruments | Derivatives Designated as Hedging Instruments | Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 3.2		$ 3.2		$ 2.3
Natural gas instruments | Not Designated as Hedging Instrument | Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0.3		$ 0.3		$ 0	$ 0.3

Derivative Financial Instrume_4

Derivative Financial Instruments - Schedule of Fair Value of Hedged Items (Details) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023	Mar. 01, 2023
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 1.1	$ 1
Liability Derivatives	4.1	2.3
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	1.1	0.9
Liability Derivatives	3.8	2.3
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	0	0.1
Liability Derivatives	0.3	0
Natural gas instruments
Derivatives, Fair Value [Line Items]
Netting of contracts in a receivable position against contracts in payable position	1.1	1
Other current assets | Natural gas instruments | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.9	0.9
Other current assets | Natural gas instruments | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	0	0.1
Other assets | Natural gas instruments | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.2
Accrued expenses and other current liabilities | Natural gas instruments | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Liability Derivatives	3.2	2.3
Accrued expenses and other current liabilities | Natural gas instruments | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Liability Derivatives	0.3	$ 0	$ 0.3
Other noncurrent liabilities | Natural gas instruments | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0.6

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Estimated Fair Values (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2024	Sep. 30, 2023
Common Stock, Large Cap US Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	30%	25%
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%	10%
Bond Funds | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	15%	10%
Short-Term Investments | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	5%	5%
Blended Funds | Mutual Fund Investments, Concentration Risk | Investment Benchmark
Liability Class:
Investment concentration risk (as a percent)	40%	45%
Fair Value, Measurements, Recurring
Asset Class:
Mutual fund investments in a non-qualified savings plan	$ 3	$ 2.6
Total Assets	3	2.7
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net		(1.4)
Liabilities related to non-qualified savings plan	(3)	(2.6)
Total Liabilities	(6)	(4)
Fair Value, Measurements, Recurring | Derivatives Designated as Hedging Instruments
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	(2.7)
Fair Value, Measurements, Recurring | Not Designated as Hedging Instrument
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	(0.3)
Fair Value, Measurements, Recurring | Natural gas instruments, net
Asset Class:
Derivatives not designated as hedging instruments - natural gas instruments, net		0.1
Fair Value, Measurements, Recurring | Level One
Asset Class:
Mutual fund investments in a non-qualified savings plan	3	2.6
Total Assets	3	2.6
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net		0
Liabilities related to non-qualified savings plan	(3)	(2.6)
Total Liabilities	(3)	(2.6)
Fair Value, Measurements, Recurring | Level One | Derivatives Designated as Hedging Instruments
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	0
Fair Value, Measurements, Recurring | Level One | Not Designated as Hedging Instrument
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	0
Fair Value, Measurements, Recurring | Level One | Natural gas instruments, net
Asset Class:
Derivatives not designated as hedging instruments - natural gas instruments, net		0
Fair Value, Measurements, Recurring | Level Two
Asset Class:
Mutual fund investments in a non-qualified savings plan	0	0
Total Assets	0	0.1
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net		(1.4)
Liabilities related to non-qualified savings plan	0	0
Total Liabilities	(3)	(1.4)
Fair Value, Measurements, Recurring | Level Two | Derivatives Designated as Hedging Instruments
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	(2.7)
Fair Value, Measurements, Recurring | Level Two | Not Designated as Hedging Instrument
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	(0.3)
Fair Value, Measurements, Recurring | Level Two | Natural gas instruments, net
Asset Class:
Derivatives not designated as hedging instruments - natural gas instruments, net		0.1
Fair Value, Measurements, Recurring | Level Three
Asset Class:
Mutual fund investments in a non-qualified savings plan	0	0
Total Assets	0	0
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net		0
Liabilities related to non-qualified savings plan	0	0
Total Liabilities	0	0
Fair Value, Measurements, Recurring | Level Three | Derivatives Designated as Hedging Instruments
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	0
Fair Value, Measurements, Recurring | Level Three | Not Designated as Hedging Instrument
Liability Class:
Derivatives designated as hedging instruments - natural gas instruments, net	$ 0
Fair Value, Measurements, Recurring | Level Three | Natural gas instruments, net
Asset Class:
Derivatives not designated as hedging instruments - natural gas instruments, net		$ 0

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
Debt Instrument [Line Items]
Increase to contingent consideration liability		$ (21,400,000)	$ 0
Fortress
Debt Instrument [Line Items]
Increase to contingent consideration liability	$ 24,300,000	$ 21,400,000
Senior Notes | 6.75% Senior Notes due December 2027
Debt Instrument [Line Items]
Stated interest rate (as a percent)	6.75%	6.75%		6.75%
Fair value of senior notes	$ 481,900,000	$ 481,900,000		$ 472,500,000
Senior Notes due 2027
Debt Instrument [Line Items]
Debt fair value amount	500,000,000	500,000,000		500,000,000
Term Loan
Debt Instrument [Line Items]
Fair value of credit agreement debt	314,700,000	314,700,000		277,100,000
Aggregate principal amount due at maturity	318,500,000	318,500,000		280,300,000
Fair Value, Measurements, Recurring
Debt Instrument [Line Items]
Mutual fund investments in a non-qualified savings plan	$ 3,000,000	$ 3,000,000		$ 2,600,000

Fair Value Measurements- Schedu

Fair Value Measurements- Schedule of Contingent Consideration (Details) - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023
Asset Acquisition, Contingent Consideration [Line Items]
Total contingent consideration	$ 13.2	$ 43.7
Accrued expenses and other current liabilities
Asset Acquisition, Contingent Consideration [Line Items]
Accrued expenses and other current liabilities	0	8.4
Other noncurrent liabilities
Asset Acquisition, Contingent Consideration [Line Items]
Other noncurrent liabilities	$ 13.2	$ 35.3

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net loss from continuing operations	$ (48)	$ (21.6)	$ (123.1)	$ (21.9)
Less: net earnings allocated to participating securities	(0.1)	(0.1)	(0.2)	(0.2)
Net loss available to common stockholders	$ (48.1)	$ (21.7)	$ (123.3)	$ (22.1)
Denominator (in thousands):
Weighted-average common shares outstanding, shares for basic earnings per share (in shares)	41,306	41,110	41,255	40,423
Weighted-average awards outstanding (in shares)	0	0	0	0
Shares for diluted earnings per share (in shares)	41,306	41,110	41,255	40,423
Basic net loss per common share (in dollars per share)	$ (1.16)	$ (0.53)	$ (2.99)	$ (0.55)
Diluted net loss per common share (in dollars per share)	$ (1.16)	$ (0.53)	$ (2.99)	$ (0.55)
Participating securities (in shares)	684,000	439,000	732,000	477,000
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive weighted options outstanding (in shares)	1,525,000	1,193,000	1,669,000	1,275,000

Related Party Disclosures (Deta

Related Party Disclosures (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended
	Mar. 20, 2024	Dec. 20, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
Related Party Transaction [Line Items]
Revenue			$ 364	$ 411.1	$ 705.7	$ 763.5
Receivables			143		143		$ 129.5
Accounts payable			88.5		88.5		116.8
Cash dividend declared (in dollars per share)	$ 0.15	$ 0.15
Payments of dividends					12.7	12.6
Koch Minerals & Trading, LLC
Related Party Transaction [Line Items]
Revenue			1	$ 0.9	1.8	$ 1.8
Receivables			0.5		0.5		$ 0.4
Accounts payable			0		0
Payments of dividends			$ 1		$ 2.1

Revision of Previously Issued_3

Revision of Previously Issued Financial Statements - Schedule of Cash Flow Classifications (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Dec. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Changes in operating assets and liabilities:
Accounts payable and accrued expenses and other current liabilities	$ (66.6)	$ (71.2)	$ 41.2
Net cash provided by operating activities	(52)	22.3	149.5
Cash flows from investing activities:
Capital expenditures	(48.9)	(65.3)	(49.3)
Net cash used in investing activities	(49.6)	$ (66.4)	(49.6)
As Previously Reported
Changes in operating assets and liabilities:
Accounts payable and accrued expenses and other current liabilities	(80.2)		35.6
Net cash provided by operating activities	(65.6)		143.9
Cash flows from investing activities:
Capital expenditures	(35.3)		(43.7)
Net cash used in investing activities	(36)		(44)
Adjustments
Changes in operating assets and liabilities:
Accounts payable and accrued expenses and other current liabilities	13.6		5.6
Net cash provided by operating activities	13.6		5.6
Cash flows from investing activities:
Capital expenditures	(13.6)		(5.6)
Net cash used in investing activities	$ (13.6)		$ (5.6)