Cash, Cash Equivalents, and Marketable Debt Securities - Schedule of Marketable Debt Securities in Continuous Loss Position (Details) $ in Millions	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities	$ 104.9	$ 78.1
Number of Marketable Debt Securities in a Loss Position \| security	108	71
Unrealized Losses	$ (0.8)
Unrealized Losses	0.8
Certificates of Deposit
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities	$ 1.7
Number of Marketable Debt Securities in a Loss Position \| security	2
U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities		$ 14.0
Number of Marketable Debt Securities in a Loss Position \| security		9
U.S. Government Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities	$ 1.1	$ 0.8
Number of Marketable Debt Securities in a Loss Position \| security	1	1
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities	$ 102.1	$ 63.3
Number of Marketable Debt Securities in a Loss Position \| security	105	61
Unrealized Losses	$ (0.8)
Unrealized Losses	$ 0.8

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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