Quarterly Results of Operations - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly results of operations
Net sales	$ 26,300	$ 28,400	$ 27,100	$ 27,100	$ 25,700	$ 26,500	$ 28,900	$ 27,900	$ 108,920	$ 108,994	$ 103,846
Gross margin	9,100	9,400	8,500	8,200	7,600	8,100	9,100	8,600	35,167	33,401	32,248
Net income (loss)	10,000	7,800	1,200	(2,200)	(5,400)	1,200	(28,800)	10,300
Net income (loss) attributable to NL stockholders	$ 9,600	$ 7,400	$ 800	$ (2,500)	$ (5,600)	$ 900	$ (29,200)	$ 10,000	$ 15,325	$ (23,909)	$ 28,499
Income (loss) per common share attributable to NL stockholders	$ 0.20	$ 0.15	$ 0.02	$ (0.05)	$ (0.11)	$ 0.02	$ (0.60)	$ 0.21	$ 0.31	$ (0.49)	$ 0.59