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Environmental Commitments and Contingencies - Additional Information (Detail)
3 Months Ended 9 Months Ended
Mar. 31, 2022
USD ($)
site
Sep. 30, 2021
USD ($)
Dec. 31, 2021
USD ($)
Environmental Commitments And Contingencies [Line Items]      
Company's exposure in number of former Manufactured Gas Plant Sites | site 7    
Environmental liabilities $ 3,271,000   $ 3,538,000
West Palm Beach Florida [Member] | Minimum [Member]      
Environmental Commitments And Contingencies [Line Items]      
Estimated costs of remediation range, minimum 3,300,000    
West Palm Beach Florida [Member] | Maximum [Member]      
Environmental Commitments And Contingencies [Line Items]      
Estimated costs of remediation range, minimum 14,200,000    
Seaford [Member] | Minimum [Member]      
Environmental Commitments And Contingencies [Line Items]      
Estimated costs of remediation range, minimum 300,000    
Seaford [Member] | Maximum [Member]      
Environmental Commitments And Contingencies [Line Items]      
Estimated costs of remediation range, minimum 900,000    
Manufactured Gas Plant [Member]      
Environmental Commitments And Contingencies [Line Items]      
Regulatory Assets for future recovery of environmental costs 1,100,000   1,300,000
FPU [Member]      
Environmental Commitments And Contingencies [Line Items]      
Environmental liabilities 4,900,000   5,200,000
Approval of recovery of environmental costs 14,000,000    
Environmental costs recovered 13,000,000 $ 12,900,000  
FPU [Member] | Manufactured Gas Plant [Member]      
Environmental Commitments And Contingencies [Line Items]      
Regulatory Assets for future recovery of environmental costs $ 1,000,000   $ 1,100,000