Fair Value Measurements - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Convertible Preferred Stock Warrant Liability
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other income, net	$ 2.3
Level 2 | Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	6.0
Level 2 | U.S. Government Debt and Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 4.0