The Company and Significant Accounting Policies - Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Money Market Account
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	$ 78.2	$ 59.9
Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets		2.8
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	10.0	25.2
Level 2 | Money Market Account
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	78.2	59.9
Level 2 | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets		2.8
Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	$ 10.0	$ 25.2