Marketable Securities - Schedule of Marketable Securities and Fair Value Measurements (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, current	$ 2.6	$ 4.4
Marketable securities, noncurrent	3.3	2.9
Fixed Income Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	1.3	2.7
Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	2.0
Common stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent		0.2
Quoted Prices in Active Markets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	2.0	0.2
Quoted Prices in Active Markets (Level 1) | Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	2.0
Quoted Prices in Active Markets (Level 1) | Common stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent		0.2
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, current	2.6	4.4
Marketable securities, noncurrent	1.3	2.7
Significant Other Observable Inputs (Level 2) | Fixed Income Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities, noncurrent	$ 1.3	$ 2.7