v3.26.1
OPERATING SEGMENTS - Schedule of Disaggregated Revenue by Product Type (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Sales to external customers $ 215.3 $ 214.6 $ 1,064.6 $ 1,016.4
Loss on sale of business, net (0.1) 0.0 14.5 0.0
Cumulative foreign currency translation adjustments 0.0 0.0 13.1 0.0
Loss on impairments 0.0 0.7 0.0 53.7
Production recall expense   0.2   2.0
Severance costs   0.3   4.3
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Wynyard SOP Business        
Segment Reporting [Line Items]        
Loss on sale of business, net     14.5  
Cumulative foreign currency translation adjustments     13.1  
Highway Salt        
Segment Reporting [Line Items]        
Sales to external customers 89.9 88.8 579.6 551.7
Consumer & Industrial Salt        
Segment Reporting [Line Items]        
Sales to external customers 84.0 77.2 308.4 289.2
SOP        
Segment Reporting [Line Items]        
Sales to external customers 41.0 48.0 171.8 173.2
Eliminations & Other        
Segment Reporting [Line Items]        
Sales to external customers 0.4 0.6 4.8 2.3
Operating Segments | Salt        
Segment Reporting [Line Items]        
Sales to external customers 173.9 166.0 888.0 840.9
Loss on sale of business, net 0.0   0.0  
Loss on impairments   0.0   0.0
Operating Segments | Plant Nutrition        
Segment Reporting [Line Items]        
Sales to external customers 37.6 44.8 165.4 164.5
Loss on sale of business, net (0.1)      
Loss on impairments   0.0   0.0
Operating Segments | Plant Nutrition | Wynyard SOP Business        
Segment Reporting [Line Items]        
Loss on sale of business, net     14.5  
Operating Segments | Highway Salt | Salt        
Segment Reporting [Line Items]        
Sales to external customers 89.9 88.8 579.6 551.7
Operating Segments | Highway Salt | Plant Nutrition        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Operating Segments | Consumer & Industrial Salt | Salt        
Segment Reporting [Line Items]        
Sales to external customers 84.0 77.2 308.4 289.2
Operating Segments | Consumer & Industrial Salt | Plant Nutrition        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Operating Segments | SOP | Salt        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Operating Segments | SOP | Plant Nutrition        
Segment Reporting [Line Items]        
Sales to external customers 41.0 48.0 171.8 173.2
Operating Segments | Eliminations & Other | Salt        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Operating Segments | Eliminations & Other | Plant Nutrition        
Segment Reporting [Line Items]        
Sales to external customers (3.4) (3.2) (6.4) (8.7)
Corporate & Other        
Segment Reporting [Line Items]        
Sales to external customers 3.8 3.8 11.2 11.0
Loss on sale of business, net 0.0   0.0  
Loss on impairments   0.7   53.7
Corporate & Other | Highway Salt        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Corporate & Other | Consumer & Industrial Salt        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Corporate & Other | SOP        
Segment Reporting [Line Items]        
Sales to external customers 0.0 0.0 0.0 0.0
Corporate & Other | Eliminations & Other        
Segment Reporting [Line Items]        
Sales to external customers $ 3.8 $ 3.8 $ 11.2 $ 11.0