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Fair Value Measurements (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	$ 1,144.6
Debt Securities, Available-for-sale	[1]	1,139.0
Fair Value, Recurring
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	[1]	1,139.0	$ 1,136.0
Fair Value, Recurring | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	[1]	551.0	531.6
Fair Value, Recurring | Municipal obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	[1]	9.5	12.1
Fair Value, Recurring | US Government Sponsored Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	[1]	281.4	255.9
Fair Value, Recurring | Foreign Government Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	[1]	3.8	12.7
Fair Value, Recurring | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	[1]	293.3	323.7
Fair Value, Recurring | Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	1,144.6	1,142.2
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	1.5	1.6
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	(7.1)	(7.8)
Debt Securities, Available-for-sale	[1]	1,139.0	1,136.0
Fair Value, Recurring | Short-term Investments [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	553.3	534.1
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	0.8	0.8
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	(3.1)	(3.3)
Debt Securities, Available-for-sale	[1]	551.0	531.6
Fair Value, Recurring | Short-term Investments [Member] | Municipal obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	9.6	12.2
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	0.0	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	(0.1)	(0.1)
Debt Securities, Available-for-sale	[1]	9.5	12.1
Fair Value, Recurring | Short-term Investments [Member] | US Government Sponsored Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	283.5	257.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	0.1	0.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	(2.2)	(1.6)
Debt Securities, Available-for-sale	[1]	281.4	255.9
Fair Value, Recurring | Short-term Investments [Member] | Foreign Government Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	3.8	12.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	0.0	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	0.0	(0.1)
Debt Securities, Available-for-sale	[1]	3.8	12.7
Fair Value, Recurring | Short-term Investments [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	[1]	294.4	325.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	[1]	0.6	0.7
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	[1]	(1.7)	(2.7)
Debt Securities, Available-for-sale	[1]	$ 293.3	$ 323.7
[1] Available-for-sale investments are included in Short-term investments in the condensed consolidated balance sheets.

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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