Quarterly Results of Operations - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly results of operations
Net sales	$ 27,400	$ 30,000	$ 32,400	$ 28,400	$ 25,100	$ 27,000	$ 30,000	$ 29,900	$ 118,217	$ 112,035	$ 108,920
Gross margin	7,900	9,600	11,200	9,500	7,400	8,200	9,500	9,700	38,271	34,825	35,167
Net income (loss)	3,100	(14,900)	(42,000)	14,700	49,600	17,800	41,600	8,800	(39,013)	117,826	16,693
Amounts attributable to NL stockholders:
Net income (loss)	$ 2,800	$ (15,400)	$ (42,600)	$ 14,200	$ 49,100	$ 17,500	$ 41,200	$ 8,300	$ (41,017)	$ 116,100	$ 15,325
Income (loss) per common share	$ 0.06	$ (0.32)	$ (0.87)	$ 0.29	$ 1.00	$ 0.36	$ 0.85	$ 0.17	$ (0.84)	$ 2.38	$ 0.31