Cash, Cash Equivalents, and Marketable Debt Securities - Schedule of Marketable Debt Securities in Continuous Loss Position (Details) $ in Millions	Jun. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities | $	$ 4.0	$ 78.1
Number of Marketable Debt Securities in a Loss Position | security	7	71
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 | $		$ 0.8
Number of Marketable Debt Securities in a Loss Position | security		1
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Fair Value of Marketable Debt Securities | $	$ 4.0	$ 63.3
Number of Marketable Debt Securities in a Loss Position | security	7	61