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