Derivative Instruments - Additional Information (Detail) MW in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) MW	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MW	2.3
Energy Hedges [Member]
Derivative [Line Items]
Proceeds from Hedge, Investing Activities	$ 36,000,000	$ 18,000,000	$ 8,000,000
Payments for (Proceeds from) Hedge, Investing Activities		2,000,000	$ 24,000,000
Interest rate swap
Derivative [Line Items]
Derivative, Notional Amount	$ 200,000,000
Fiscal Year 2020 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MW	2.1
Fiscal Year 2021 [Member] [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MW	0.2
Fair Value, Inputs, Level 2 [Member] | Interest rate swap
Derivative [Line Items]
Derivative Liability	$ 10,000,000	$ 2,000,000