CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 13,866	$ 2,502
Other comprehensive income (loss), net of tax:
Currency translation	545	(10,118)
Defined benefit pension plans	1,151	1,043
Other postretirement benefit plans	(71)	(80)
Total other comprehensive income (loss), net	1,625	(9,155)
Comprehensive income (loss)	15,491	(6,653)
Comprehensive income attributable to noncontrolling interest	609	592
Comprehensive income (loss) attributable to NL stockholders	$ 14,882	$ (7,245)