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Commitments and Contingencies - Additional Information (Detail) |  | 204 Months Ended |
--- | --- | --- | ---
Jan. 06, 2017 USD ($) Segment | Dec. 31, 2016 USD ($) | Aug. 31, 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 |  |  | $ 8,400,000
Portland Harbor Superfund 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 Superfund Site | Minimum |  |  |
Commitments and Contingencies Disclosure [Line Items] |  |  |
Accuracy of cost estimate | (30.00%) |  |
Portland Harbor Superfund Site | Maximum |  |  |
Commitments and Contingencies Disclosure [Line Items] |  |  |
Accuracy of cost estimate | 50.00% |  |

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