Investments - Schedule of Fair Value of Cash Equivalents, Long and Short Term Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Amortized Cost
Schedule of Investments [Line Items]
Total cash equivalents and investments	$ 122.4	$ 154.9
Less: cash equivalents	(58.6)	(51.8)
Total Investments	63.8	103.1
Amortized Cost | Commercial Bonds and Paper | Fair Value, Inputs, Level 2
Schedule of Investments [Line Items]
Total cash equivalents and investments	43.3	66.8
Amortized Cost | Money Market Funds | Fair Value, Inputs, Level 1
Schedule of Investments [Line Items]
Total cash equivalents and investments	69.6	51.8
Amortized Cost | U.S. Treasuries | Fair Value, Inputs, Level 2
Schedule of Investments [Line Items]
Total cash equivalents and investments	9.5	36.3
Gross Unrealized Holding Gains (Losses)
Schedule of Investments [Line Items]
Total cash equivalents and investments	0.2	(1.2)
Total Investments	0.2	(1.2)
Gross Unrealized Holding Gains (Losses) | Commercial Bonds and Paper | Fair Value, Inputs, Level 2
Schedule of Investments [Line Items]
Total cash equivalents and investments	0.1	(0.6)
Gross Unrealized Holding Gains (Losses) | U.S. Treasuries | Fair Value, Inputs, Level 2
Schedule of Investments [Line Items]
Total cash equivalents and investments	0.1	(0.6)
Estimated Fair Value
Schedule of Investments [Line Items]
Total cash equivalents and investments	122.6	153.7
Less: cash equivalents	(58.6)	(51.8)
Total Investments	64.0	101.9
Estimated Fair Value | Commercial Bonds and Paper | Fair Value, Inputs, Level 2
Schedule of Investments [Line Items]
Total cash equivalents and investments	43.4	66.2
Estimated Fair Value | Money Market Funds | Fair Value, Inputs, Level 1
Schedule of Investments [Line Items]
Total cash equivalents and investments	69.6	51.8
Estimated Fair Value | U.S. Treasuries | Fair Value, Inputs, Level 2
Schedule of Investments [Line Items]
Total cash equivalents and investments	$ 9.6	$ 35.7