Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

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Commitments, Contingencies and Legal Proceedings - Narrative (Detail) $ in Thousands	6 Months Ended	9 Months Ended
	Jun. 30, 2021 Operable_Unit	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Commitments Contingencies And Litigation [Line Items]
Number of operable units \| Operable_Unit	5
Term of agreement with third party for monitoring and maintenance in OU1-OU4a		30 years
Difference recorded in escrow account		$ 1,600
Total amount available in escrow account		8,800
Reserve for environmental liabilities, current portion		2,529	$ 3,700
Other Long-Term Liabilities
Commitments Contingencies And Litigation [Line Items]
Reserve for environmental liabilities, remaining portion		$ 14,300
Minimum
Commitments Contingencies And Litigation [Line Items]
Period over which cash expenditure to be incurred for monitoring activities		30 years