Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2021

Investments Debt And Equity Securities [Abstract]

Schedule of Marketable Securities

	Fair value measurement level	Market value		Cost basis		Unrealized gain (loss)
		(In thousands)
December 31, 2020
Valhi common stock	1	$	18,206	$	24,347	$	(6,141	)
September 30, 2021
Valhi common stock	1	$	27,943	$	24,347	$	3,596