Quarterly Results of Operations - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly results of operations
Net sales	$ 25,100	$ 27,000	$ 30,000	$ 29,900	$ 26,300	$ 28,400	$ 27,100	$ 27,100	$ 112,035	$ 108,920	$ 108,994
Gross margin	7,400	8,200	9,500	9,700	9,100	9,400	8,500	8,200	34,825	35,167	33,401
Net income (loss)	49,600	17,800	41,600	8,800	10,000	7,800	1,200	(2,200)
Amounts attributable to NL stockholders:
Net income (loss)	$ 49,100	$ 17,500	$ 41,200	$ 8,300	$ 9,600	$ 7,400	$ 800	$ (2,500)	$ 116,100	$ 15,325	$ (23,909)
Income (loss) per common share	$ 1.00	$ 0.36	$ 0.85	$ 0.17	$ 0.20	$ 0.15	$ 0.02	$ (0.05)	$ 2.38	$ 0.31	$ (0.49)