Commitments and Contingencies - Additional Information (Detail) - USD ($)		9 Months Ended
Jun. 24, 2019	Sep. 30, 2019	Dec. 31, 2018
Commitments and Contingencies Additional Textual [Abstract]
Remaining environmental accrued liability recorded		$ 0	$ 0
Beta's decommissioning obligations, previously supported by surety bonds		71,300,000
Beta's decommissioning obligations, cash		90,200,000
Proceeds from Beta Decommissioning Trust account	$ 90,000,000	0
Beta's decommissioning obligations, full supported by surety bonds		161,300,000
Beta's decommissioning remaining obligations, cash		$ 300,000

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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