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Financial Instruments - Summary of Valuation of Short-term Investments and Financial Instruments (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable securities, current | $ 4.4 | $ 2.1
Marketable securities, noncurrent | 2.9 | 6.2
Quoted Prices in Active Markets (Level 1) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable securities, noncurrent | 0.2 | 1.3
Significant Other Observable Inputs (Level 2) |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Marketable securities, current | 4.4 | 2.1
Marketable securities, noncurrent | $ 2.7 | $ 4.9

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