CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 28,035	$ (39,013)	$ 117,826
Other comprehensive income (loss), net of tax:
Currency translation	(409)	(7,967)	11,392
Defined benefit pension plans	(2,971)	(2,335)	3,759
Marketable equity securities			25,596
Interest rate swap			390
Other	(40)	(162)	(28)
Total other comprehensive income (loss), net	(3,420)	(10,464)	41,109
Comprehensive income (loss)	24,615	(49,477)	158,935
Comprehensive income attributable to noncontrolling interest	2,191	2,004	1,726
Comprehensive income (loss) attributable to NL stockholders	$ 22,424	$ (51,481)	$ 157,209