Accounts Payable and Accrued Liabilities - Schedule of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts payable:
Accounts payable	$ 117.6	$ 144.7
Current accrued liabilities:
Employee benefits	37.5	30.6
Operating lease liabilities	6.7	6.2
Accrued sales discounts and rebates	30.2	33.7
Deferred income	20.1	10.3
Environmental remediation and related costs	3.4	4.5	$ 6.5
Interest	5.7	5.2
Other	39.4	40.0
Total	143.0	130.5
Noncurrent accrued liabilities:
Other postretirement benefits	10.8	10.5
Operating lease liabilities	18.8	22.2
Reserve for uncertain tax positions	6.8	13.6
Deferred income	58.9	47.4
Employee benefits	6.2	6.0
Insurance claims and expenses	39.3	11.0
Deferred payment obligation	1.3	9.9
Accrued development costs	24.6	8.3
Other	7.8	8.2
Total	174.5	137.1
Kronos Worldwide, Inc.
Accounts payable:
Accounts payable	111.0	137.2
CompX
Accounts payable:
Accounts payable	2.6	2.5
BMI/LandWell
Accounts payable:
Accounts payable	3.6	3.7
NL
Accounts payable:
Accounts payable		0.9
Other
Accounts payable:
Accounts payable	$ 0.4	$ 0.4