CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Net sales	$ 34,556	$ 28,426	$ 106,733	$ 84,537
Cost of sales	23,634	21,098	73,470	59,412
Gross margin	10,922	7,328	33,263	25,125
Selling, general and administrative expense	5,791	5,246	16,557	15,654
Other operating income (expense):
Insurance recoveries	24		56	108
Corporate expense	(2,871)	(2,390)	(7,619)	(7,339)
Income (loss) from operations	2,284	(308)	9,143	2,240
Equity in earnings of Kronos Worldwide, Inc.	10,934	2,475	24,718	16,333
Other income (expense):
Interest and dividend income	387	470	1,250	2,102
Marketable equity securities	(1,198)	3,210	9,737	(11,115)
Other components of net periodic pension and OPEB cost	(196)	(208)	(463)	(624)
Interest expense	(299)	(352)	(896)	(1,054)
Income before income taxes	11,912	5,287	43,489	7,882
Income tax expense (benefit)	1,054	1,163	5,460	(3,616)
Net income	10,858	4,124	38,029	11,498
Noncontrolling interest in net income of subsidiary	545	252	1,762	1,127
Net income attributable to NL stockholders	$ 10,313	$ 3,872	$ 36,267	$ 10,371
Amounts attributable to NL stockholders:
Basic and diluted net income per share	$ 0.21	$ 0.08	$ 0.74	$ 0.21
Weighted average shares used in the calculation of net income per share	48,803	48,789	48,795	48,772