Business Segment Information - Additional Information (Detail)	Sep. 30, 2018
Kronos Worldwide, Inc.
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	50.00%
Indirect controlling interest in subsidiary	30.00%
NL
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	83.00%
LandWell
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	27.00%
Indirect controlling interest in subsidiary	50.00%
BMI
Segment Reporting Information [Line Items]
Direct ownership percentage by parent	63.00%