Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration	$ 1.6	$ 8.1
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration		8.1
Fair Value, Measurements, Recurring | Money Market Account
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	21.3	34.6
Fair Value, Measurements, Recurring | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	6.1	8.2
Fair Value, Measurements, Recurring | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	85.6	124.2
Fair Value, Measurements, Recurring | 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	21.3	34.6
Fair Value, Measurements, Recurring | 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	6.1	8.2
Fair Value, Measurements, Recurring | Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value and Carrying Value on Assets	$ 85.6	124.2
Fair Value, Measurements, Recurring | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration		$ 8.1