CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss	Noncontrolling interest in subsidiary
Beginning Balance at Dec. 31, 2015	$ 165,251	$ 6,086	$ 300,543	$ 88,679	$ (245,358)	$ 15,301
Net income (loss)	16,693			15,325		1,368
Other comprehensive income (loss), net of tax	12,512				12,512
Issuance of NL common stock	37	2	35
Cash dividends	(332)					(332)
Other, net	109		96			13
Ending Balance at Dec. 31, 2016	194,270	6,088	300,674	104,004	(232,846)	16,350
Net income (loss)	117,826			116,100		1,726
Other comprehensive income (loss), net of tax	41,109				41,109
Issuance of NL common stock	83	1	82
Cash dividends	(333)					(333)
Other, net	123		110			13
Ending Balance at Dec. 31, 2017	353,078	6,089	300,866	220,104	(191,737)	17,756
Change in accounting principle-ASU 2016-01 at Dec. 31, 2017				46,069	(46,069)
Balance at January 1, 2018, as adjusted at Dec. 31, 2017	353,078	6,089	300,866	266,173	(237,806)	17,756
Net income (loss)	(39,013)			(41,017)		2,004
Other comprehensive income (loss), net of tax	(10,464)				(10,464)
Issuance of NL common stock	120	1	119
Cash dividends	(335)					(335)
Other, net	172		154			18
Ending Balance at Dec. 31, 2018	$ 303,558	$ 6,090	$ 301,139	$ 225,156	$ (248,270)	$ 19,443