Quarterly Results of Operations - Quarterly Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly results of operations
Net sales	$ 24,744	$ 26,473	$ 26,848	$ 25,781	$ 22,344	$ 24,209	$ 24,039	$ 21,453	$ 103,846	$ 92,045	$ 83,196
Gross margin	7,744	8,142	8,613	7,749	6,430	7,514	7,610	6,020	32,248	27,574	24,327
Net income (loss)	5,610	14,180	5,806	4,034	(32,843)	(5,684)	(14,018)	(1,998)
Net loss attributable to NL stockholders	$ 5,383	$ 13,889	$ 5,472	$ 3,755	$ (33,020)	$ (5,940)	$ (14,255)	$ (2,118)	$ 28,499	$ (55,333)	$ 74,536
Loss per common share attributable to NL stockholders	$ 0.11	$ 0.29	$ 0.11	$ 0.08	$ (0.68)	$ (0.12)	$ (0.29)	$ (0.04)