Other Income, Net - Additional Information (Detail) $ in Millions		3 Months Ended			12 Months Ended
	May 30, 2018 USD ($)	Dec. 31, 2018 USD ($) Parcel	Sep. 30, 2018 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) Parcel	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Disclosure Other Income Net Additional Information Detail [Line Items]
Dividends and interest income					$ 26.1	$ 29.4	$ 26.7
Gain on securities transaction recognized					$ 12.4	0.1	0.5
Number of land parecels | Parcel		2			2
Net proceeds					$ 19.5
Pre-tax gain on sale of land		$ 11.9
Income received from settlement of business interruption insurance claim							4.3
Tremont
Disclosure Other Income Net Additional Information Detail [Line Items]
Net proceeds		18.9
Kronos Worldwide, Inc. | Other Income | Insurance Claim Arising In 2014
Disclosure Other Income Net Additional Information Detail [Line Items]
Income received from settlement of business interruption insurance claim							3.4
Kronos Worldwide, Inc. | Other Income | Insurance Claim Arising In 2015
Disclosure Other Income Net Additional Information Detail [Line Items]
Income received from settlement of business interruption insurance claim				$ 0.9
Promissory Note | Tremont
Disclosure Other Income Net Additional Information Detail [Line Items]
Principal payment of debt		2.2			3.7	1.5
Amalgamated Sugar Company LLC
Disclosure Other Income Net Additional Information Detail [Line Items]
Dividends and interest income					16.9	$ 25.4	$ 25.4
Snake River
Disclosure Other Income Net Additional Information Detail [Line Items]
Gain on securities transaction recognized	$ 12.5		$ 12.5		$ 12.5
NL
Disclosure Other Income Net Additional Information Detail [Line Items]
Net proceeds		$ 0.6