Marketable Securities - Schedule of Marketable Securities and Fair Value Measurements (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, current	$ 4.4	$ 2.0
Marketable securities, noncurrent	253.5	254.9
Fixed Income Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	2.9	1.4
Mutual Funds and Common Stocks
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	0.6	3.5
Amalgamated Sugar Company LLC
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	250.0	250.0
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	0.6	3.5
Level 1 | Mutual Funds and Common Stocks
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	0.6	3.5
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, current	4.4	2.0
Marketable securities, noncurrent	2.9	1.4
Level 2 | Fixed Income Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	2.9	1.4
Level 3 Inputs
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	250.0	250.0
Level 3 Inputs | Amalgamated Sugar Company LLC
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	$ 250.0	$ 250.0