v3.26.1
OPERATING SEGMENTS - Schedule of Segment Information (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Sep. 30, 2025
Segment Reporting [Line Items]          
Sales $ 215.3 $ 214.6 $ 1,064.6 $ 1,016.4  
Gross profit 37.9 41.2 184.1 152.3  
Selling, general and administrative expenses 27.0 24.0 80.6 86.9  
Loss on impairments 0.0 0.7 0.0 53.7  
Other operating expense (income) 0.0 0.6 0.0 (1.6)  
Operating income (loss) 10.9 15.9 103.5 13.3  
Depreciation, depletion and amortization 25.6 23.2 80.2 76.5  
(Gain) loss on sale of business, net (0.1) 0.0 14.5 0.0  
Capital expenditures 21.1 18.0 62.1 53.8  
Total assets (as of end of period) 1,353.5 1,537.4 1,353.5 1,537.4 $ 1,519.4
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Wynyard SOP Business          
Segment Reporting [Line Items]          
(Gain) loss on sale of business, net     14.5    
Shipping and handling cost          
Segment Reporting [Line Items]          
Cost 64.0 56.7 314.1 288.7  
Product cost          
Segment Reporting [Line Items]          
Cost 113.4 116.7 566.4 575.4  
Operating Segments | Salt          
Segment Reporting [Line Items]          
Sales 173.9 166.0 888.0 840.9  
Gross profit 27.6 34.4 156.1 147.7  
Selling, general and administrative expenses 6.4 6.2 20.6 22.7  
Loss on impairments   0.0   0.0  
Other operating expense (income)   0.1   0.6  
Operating income (loss) 21.2 28.1 135.5 124.4  
Depreciation, depletion and amortization 17.7 17.5 53.8 52.4  
(Gain) loss on sale of business, net 0.0   0.0    
Capital expenditures 15.5 14.6 46.5 42.1  
Total assets (as of end of period) 894.7 1,032.1 894.7 1,032.1  
Operating Segments | Salt | Shipping and handling cost          
Segment Reporting [Line Items]          
Cost 58.8 50.0 291.3 263.2  
Operating Segments | Salt | Product cost          
Segment Reporting [Line Items]          
Cost 87.5 81.6 440.6 430.0  
Operating Segments | Plant Nutrition          
Segment Reporting [Line Items]          
Sales 37.6 44.8 165.4 164.5  
Gross profit 8.9 5.7 24.1 3.6  
Selling, general and administrative expenses 1.1 0.5 3.3 3.3  
Loss on impairments   0.0   0.0  
Other operating expense (income)   0.0   0.0  
Operating income (loss) 7.8 5.2 20.8 0.3  
Depreciation, depletion and amortization 7.2 6.2 23.9 21.1  
(Gain) loss on sale of business, net (0.1)        
Capital expenditures 3.9 2.9 13.1 9.1  
Total assets (as of end of period) 326.7 354.0 326.7 354.0  
Operating Segments | Plant Nutrition | Wynyard SOP Business          
Segment Reporting [Line Items]          
(Gain) loss on sale of business, net     14.5    
Operating Segments | Plant Nutrition | Shipping and handling cost          
Segment Reporting [Line Items]          
Cost 5.2 6.7 22.8 25.5  
Operating Segments | Plant Nutrition | Product cost          
Segment Reporting [Line Items]          
Cost 23.5 32.4 118.5 135.4  
Corporate & Other          
Segment Reporting [Line Items]          
Sales 3.8 3.8 11.2 11.0  
Gross profit 1.4 1.1 3.9 1.0  
Selling, general and administrative expenses 19.5 17.3 56.7 60.9  
Loss on impairments   0.7   53.7  
Other operating expense (income)   0.5   (2.2)  
Operating income (loss) (18.1) (17.4) (52.8) (111.4)  
Depreciation, depletion and amortization 0.7 (0.5) 2.5 3.0  
(Gain) loss on sale of business, net 0.0   0.0    
Capital expenditures 1.7 0.5 2.5 2.6  
Total assets (as of end of period) 132.1 151.3 132.1 151.3  
Corporate & Other | Shipping and handling cost          
Segment Reporting [Line Items]          
Cost 0.0 0.0 0.0 0.0  
Corporate & Other | Product cost          
Segment Reporting [Line Items]          
Cost 2.4 2.7 7.3 10.0  
Intersegment Eliminations          
Segment Reporting [Line Items]          
Sales (3.4) (3.2) (6.4) (8.7)  
Intersegment Eliminations | Salt          
Segment Reporting [Line Items]          
Sales 0.0 0.0 0.0 0.0  
Intersegment Eliminations | Plant Nutrition          
Segment Reporting [Line Items]          
Sales $ 3.4 $ 3.2 $ 6.4 $ 8.7