Earnings Per Share - Reconciliation of Numerator Used in Calculation of Earnings (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share [Line Items]
Net income attributable to NL stockholders	$ 17,500	$ 10,000	$ 26,000	$ 21,000	$ 19,900	$ 27,700	$ 16,900	$ 17,200	$ 74,536	$ 81,657	$ 70,381
Paid-in capital adjustment											(2,513)
Adjusted net income attributable to NL stockholders									$ 74,536	$ 81,657	$ 67,868