CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Net sales	$ 35,924	$ 32,311
Cost of sales	24,889	21,880
Gross margin	11,035	10,431
Selling, general and administrative expense	5,218	5,411
Other operating income (expense):
Insurance recoveries	25	22
Corporate expense	(1,870)	(2,508)
Income from operations	3,972	2,534
Equity in earnings of Kronos Worldwide, Inc.	5,968	8,207
Other income (expense):
Interest and dividend income	440	1,131
Marketable equity securities	6,360	(12,073)
Other components of net periodic pension and OPEB cost	(71)	(208)
Interest expense	(298)	(352)
Income (loss) before income taxes	16,371	(761)
Income tax expense (benefit)	2,505	(3,263)
Net income	13,866	2,502
Noncontrolling interest in net income of subsidiary	609	592
Net income attributable to NL stockholders	$ 13,257	$ 1,910
Amounts attributable to NL stockholders:
Basic and diluted net income per share	$ 0.27	$ 0.04
Weighted average shares used in the calculation of net income per share	48,789	48,756