Marketable Securities - Additional Information (Detail) - Valhi Inc - Common stock - $ / shares shares in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Number of shares owned	1.2	1.2
Quoted marked price per share	$ 23.33	$ 15.20

Balance held at close of period in number of shares.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Column B))
-URI http://asc.fasb.org/extlink&oid=122147990&loc=d3e611197-123010

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant