Quarterly Results of Operations - Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly results of operations
Net sales	$ 29,600	$ 29,700	$ 33,700	$ 31,200	$ 27,400	$ 30,000	$ 32,400	$ 28,400	$ 124,243	$ 118,217	$ 112,035
Gross margin	9,000	9,400	11,000	9,600	7,900	9,600	11,200	9,500	38,963	38,271	34,825
Net income (loss)	6,700	(1,000)	6,600	15,700	3,100	(14,900)	(42,000)	14,700	28,035	(39,013)	117,826
Amounts attributable to NL stockholders:
Net income (loss)	$ 6,300	$ (1,600)	$ 5,900	$ 15,200	$ 2,800	$ (15,400)	$ (42,600)	$ 14,200	$ 25,844	$ (41,017)	$ 116,100
Income (loss) per common share	$ 0.13	$ (0.03)	$ 0.12	$ 0.31	$ 0.06	$ (0.32)	$ (0.87)	$ 0.29	$ 0.53	$ (0.84)	$ 2.38