Commitments and Contingencies - Additional Information (Detail)		204 Months Ended
	Jan. 06, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Feb. 28, 2021 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Remedial investigation and feasibility study		$ 110,000,000
Performance Guarantee
Commitments and Contingencies Disclosure [Line Items]
Letter of credit facility outstanding amount			$ 27,900,000
Portland Harbor Site
Commitments and Contingencies Disclosure [Line Items]
Number of sediment decision units | Segment	13
Estimated undiscounted cost	$ 1,700,000,000
Period for remedial action	13 years
Period for monitoring	30 years
New data collection period to reflect actual cost prior to final remedy design	2 years
Portland Harbor Site | Minimum
Commitments and Contingencies Disclosure [Line Items]
Accuracy of cost estimate	(30.00%)
Portland Harbor Site | Maximum
Commitments and Contingencies Disclosure [Line Items]
Accuracy of cost estimate	50.00%