CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 10,858	$ 4,124	$ 38,029	$ 11,498
Other comprehensive income (loss), net of tax:
Currency translation	(1,859)	2,426	(912)	(3,328)
Defined benefit pension plans	1,133	1,075	3,428	3,149
Other postretirement benefit plans	(65)	(70)	(200)	(221)
Total other comprehensive income (loss), net	(791)	3,431	2,316	(400)
Comprehensive income	10,067	7,555	40,345	11,098
Comprehensive income attributable to noncontrolling interest	545	252	1,762	1,127
Comprehensive income attributable to NL stockholders	$ 9,522	$ 7,303	$ 38,583	$ 9,971