Marketable Securities - Schedule of Marketable Securities (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Market value, available for sale securities, current	$ 2.5	$ 3.0
Market value, available for sale securities, noncurrent	4.8	255.7
Non Current Assets
Schedule Of Available For Sale Securities [Line Items]
Market value, available for sale securities, noncurrent	4.8
Cost basis	5.2	255.9
Unrealized losses, net	(0.4)	(0.2)
Current Assets
Schedule Of Available For Sale Securities [Line Items]
Cost basis	2.5	3.0
Unrealized losses, net	$ 0.0	0.0
Other \| Non Current Assets
Schedule Of Available For Sale Securities [Line Items]
Market value, available for sale securities, noncurrent		5.7
Cost basis		5.9
Unrealized losses, net		(0.2)
Amalgamated Sugar Company LLC \| Non Current Assets
Schedule Of Available For Sale Securities [Line Items]
Market value, available for sale securities, noncurrent		250.0
Cost basis		250.0
Unrealized losses, net		$ 0.0

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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