Investments - Summary of Amortized Cost, Gross Unrealized Gains and Losses, Fair Value and Level in Fair Value Hierarchy for Investments (Details) - Short-term investments - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 17.5	$ 40.1
Gross Unrealized Gains	0.0	0.3
Fair Value	17.5	40.4
Level 1 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	15.0	35.3
Level 2 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2.5	5.1
U.S. government and agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	15.0	35.1
Gross Unrealized Gains	0.0	0.2
Fair Value	15.0	35.3
U.S. government and agency bonds | Level 1 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	15.0	35.3
U.S. government and agency bonds | Level 2 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0.0	0.0
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	2.0	2.8
Gross Unrealized Gains	0.0	0.1
Fair Value	2.0	2.9
Corporate bonds | Level 1 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0.0	0.0
Corporate bonds | Level 2 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2.0	2.9
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	0.5	2.2
Gross Unrealized Gains	0.0	0.0
Fair Value	0.5	2.2
Certificates of deposit | Level 1 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0.0	0.0
Certificates of deposit | Level 2 | Recurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 0.5	$ 2.2