Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2017	Apr. 30, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.											$ 17,961	$ 15,849
U.S. federal corporate income tax rate			21.00%				35.00%				21.00%	35.00%	35.00%
Deferred income tax benefit from change in enacted tax rate													$ (37,500)
Income tax expense (benefit)			$ (6,158)				$ 6,466				$ (15,416)	$ 28,923
Current payable to affiliate			1,600			$ 429			$ 429		1,600		429
Kronos
Income Tax Disclosure [Line Items]
Dividends received from Kronos Worldwide, Inc.											18,000	$ 15,800
Kronos | Expected Future Periods Net Operating Loss Utilization
Income Tax Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance	$ (149,900)
Kronos | Effect of Currency Exchange Rates
Income Tax Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance													13,700
Kronos | German | Expected Future Periods Net Operating Loss Utilization
Income Tax Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance	(141,900)
Kronos | German | Corporate Tax Purposes
Income Tax Disclosure [Line Items]
Net operating loss carryforwards						652,000			652,000				652,000
Kronos | German | Trade Tax Purposes
Income Tax Disclosure [Line Items]
Net operating loss carryforwards						500			500				500
Kronos | Belgium | Expected Future Periods Net Operating Loss Utilization
Income Tax Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance	$ (8,000)
Kronos | Belgium | Corporate Tax Purposes
Income Tax Disclosure [Line Items]
Net operating loss carryforwards						50,000			50,000				50,000
Kronos | Non-US
Income Tax Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance													$ (186,700)
Kronos | Non-US | Current Periods Net Operating Loss Utilization
Income Tax Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance							(7,800)	$ (7,700)	$ (24,100)	$ (12,700)
Kronos | European and Candadian Subsidiaries | Undistributed Earnings Previously Considered to be Permanently Reinvested
Income Tax Disclosure [Line Items]
Aggregate provisional non-cash deferred income tax expense (benefit)						4,500					$ 2,500
Kronos European Subsidiaries | Valhi
Income Tax Disclosure [Line Items]
Income tax liability payable period											8 years
Kronos European Subsidiaries | Valhi | Income Tax Payable
Income Tax Disclosure [Line Items]
Payable to affiliate			63,800								$ 63,800
Noncurrent payable to affiliate			58,100								58,100
Current payable to affiliate			5,700								5,700
Kronos European Subsidiaries | Transition Tax
Income Tax Disclosure [Line Items]
Currently payable (receivable)						$ 76,200
Current income tax expense payment period						8 years
Income tax expense (benefit)			1,700
Prior tax installments payments			10,700								$ 10,700
Kronos European Subsidiaries | Transition Tax | 2017 Tax Year
Income Tax Disclosure [Line Items]
Current income tax expense payable in next fiscal year		$ 6,100
Kronos European Subsidiaries | Transition Tax | 2018 Tax Year
Income Tax Disclosure [Line Items]
Current income tax expense payable in next fiscal year			$ 4,600	$ 4,600
Kronos Canadian Subsidiary | Canada-Germany APA
Income Tax Disclosure [Line Items]
Non-cash income tax benefit							$ 8,100
Kronos Canadian Subsidiary | Earliest Tax Year | Canada-Germany APA | Canada Revenue Agency
Income Tax Disclosure [Line Items]
Effective tax year							2005
Kronos Canadian Subsidiary | Latest Tax Year | Canada-Germany APA | Canada Revenue Agency
Income Tax Disclosure [Line Items]
Effective tax year							2017
Kronos Canadian Subsidiary | German | Canada-Germany APA
Income Tax Disclosure [Line Items]
Non-cash income tax benefit							$ 2,600
Cash tax refund							$ 600
Kronos German Subsidiary | Earliest Tax Year | Germany- Canada APA | Germany Revenue Agency
Income Tax Disclosure [Line Items]
Effective tax year					2005
Kronos German Subsidiary | Latest Tax Year | Germany- Canada APA | Germany Revenue Agency
Income Tax Disclosure [Line Items]
Effective tax year					2017
Kronos Canadian And German Subsidiaries | Germany- Canada APA
Income Tax Disclosure [Line Items]
Non-cash income tax benefit					$ 1,400