Income taxes - Additional Information (Detail) - USD ($)	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.	$ 13,384,000	$ 12,678,000
Kronos
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.	$ 13,400,000	$ 12,700,000

Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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