CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Net sales	$ 36,253	$ 23,800	$ 72,177	$ 56,111
Cost of sales	24,947	16,434	49,836	38,314
Gross margin	11,306	7,366	22,341	17,797
Selling, general and administrative expense	5,548	4,997	10,766	10,408
Other operating income (expense):
Insurance recoveries	7	86	32	108
Corporate expense	(2,878)	(2,441)	(4,748)	(4,949)
Income from operations	2,887	14	6,859	2,548
Equity in earnings of Kronos Worldwide, Inc.	7,816	5,651	13,784	13,858
Other income (expense):
Interest and dividend income	423	501	863	1,632
Marketable equity securities	4,575	(2,252)	10,935	(14,325)
Other components of net periodic pension and OPEB cost	(196)	(208)	(267)	(416)
Interest expense	(299)	(350)	(597)	(702)
Income before income taxes	15,206	3,356	31,577	2,595
Income tax expense (benefit)	1,901	(1,516)	4,406	(4,779)
Net income	13,305	4,872	27,171	7,374
Noncontrolling interest in net income of subsidiary	608	283	1,217	875
Net income attributable to NL stockholders	$ 12,697	$ 4,589	$ 25,954	$ 6,499
Amounts attributable to NL stockholders:
Basic and diluted net income per share	$ 0.26	$ 0.09	$ 0.53	$ 0.13
Weighted average shares used in the calculation of net income per share	48,795	48,771	48,792	48,763