The Company and Significant Accounting Policies - Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent Consideration	$ 8.5	$ 8.1
Money Market Account
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	36.7	34.6
Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	7.6	8.2
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	115.0	124.2
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	36.7	34.6
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	7.6	8.2
Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	115.0	124.2
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent Consideration	$ 8.5	$ 8.1