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Investments in Marketable Securities - Debt Securities, Available-for-Sale (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Available-for-sale
Cost	$ 252.9	$ 252.3
Unrealized losses	(0.8)	(1.3)
Fair value	252.1	251.0
Trading
Cost	20.6	19.7
Unrealized losses	(1.5)	(1.7)
Fair value	$ 19.1	$ 18.0

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Debt Securities, Trading, Accumulated Gross Unrealized Loss, Before Tax

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Amount, before tax, of unrealized loss 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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Amount of 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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