Marketable Securities (Tables)

3 Months Ended

Mar. 31, 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	)
March 31, 2021
Valhi common stock	1	$	24,566	$	24,347	$	219