CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 13,305	$ 4,872	$ 27,171	$ 7,374
Other comprehensive income (loss), net of tax:
Currency translation	402	4,364	947	(5,754)
Defined benefit pension plans	1,144	1,031	2,295	2,074
Other postretirement benefit plans	(64)	(71)	(135)	(151)
Total other comprehensive income (loss), net	1,482	5,324	3,107	(3,831)
Comprehensive income	14,787	10,196	30,278	3,543
Comprehensive income attributable to noncontrolling interest	608	283	1,217	875
Comprehensive income attributable to NL stockholders	$ 14,179	$ 9,913	$ 29,061	$ 2,668