CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (39,013)	$ 117,826	$ 16,693
Other comprehensive income (loss), net of tax:
Marketable equity securities		25,596	20,278
Currency translation	(7,967)	11,392	(3,475)
Interest rate swap		390	55
Defined benefit pension plans	(2,335)	3,759	(3,998)
Other	(162)	(28)	(348)
Total other comprehensive income (loss), net	(10,464)	41,109	12,512
Comprehensive income (loss)	(49,477)	158,935	29,205
Comprehensive income attributable to noncontrolling interest	2,004	1,726	1,368
Comprehensive income (loss) attributable to NL stockholders	$ (51,481)	$ 157,209	$ 27,837