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Commitments, Contingencies and Legal Proceedings - Schedule of Reserves (Detail) - USD ($) $ in Thousands | 9 Months Ended
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Sep. 30, 2021 | Sep. 30, 2020
Government Oversight Reserves Rollforward |  |
Beginning balance | $ 18,455 | $ 21,870
Payments | (1,780) | (3,243)
Accretion | 152 | 155
Ending balance | $ 16,827 | $ 18,782

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 + Details
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