Commitments, Contingencies and Legal Proceedings - Schedule of Reserves (Detail) - USD ($) $ in Thousands	9 Months Ended
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

Total costs accrued as of the balance sheet date for environmental loss contingencies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

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