Cash and Cash Equivalents - Components (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash	$ 204.9
Cash Equivalents, at Carrying Value [Abstract]
Total cash equivalents	100.0
Cash and cash equivalents	304.9	$ 41.4
Corporate debt securities
Cash Equivalents, at Carrying Value [Abstract]
Total cash equivalents	17.6
Money market mutual funds
Cash Equivalents, at Carrying Value [Abstract]
Total cash equivalents	$ 82.4

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