Allowance for Doubtful Accounts - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Recoveries	$ 0.6	$ 0.9	$ 0.8
Provision for Bad Debt	6.4	6.7	5.6
Allowance for doubtful accounts	2.4	2.6	3.3	$ 3.3
Unbilled Revenues
Financing Receivable, Impaired [Line Items]
Allowance for doubtful accounts	0.1	0.1	0.1
Accounts Receivable
Financing Receivable, Impaired [Line Items]
Allowance for doubtful accounts	2.3	2.5
Regulatory Assets Harship Accounts
Financing Receivable, Impaired [Line Items]
Recoveries	6.0	5.8
Energy Commodity
Financing Receivable, Impaired [Line Items]
Provision for Bad Debt	$ 3.8	$ 3.8	$ 2.4