Quarterly Results of Operations - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly results of operations
Net sales	$ 25,700	$ 26,500	$ 28,900	$ 27,900	$ 24,700	$ 26,500	$ 26,800	$ 25,800	$ 108,994	$ 103,846	$ 92,045
Gross margin	7,600	8,100	9,100	8,600	7,700	8,200	8,600	7,700	33,401	32,248	27,574
Net income (loss)	(5,400)	1,200	(28,800)	10,300	5,600	14,100	5,800	4,100
Net income (loss) attributable to NL stockholders	$ (5,600)	$ 900	$ (29,200)	$ 10,000	$ 5,400	$ 13,900	$ 5,500	$ 3,700	$ (23,909)	$ 28,499	$ (55,333)
Income (loss) per common share attributable to NL stockholders	$ (0.11)	$ 0.02	$ (0.60)	$ 0.21	$ 0.11	$ 0.29	$ 0.11	$ 0.08