Preferred and Common Stock Warrants - Redeemable Convertible Preferred Stock Warrants (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Class of Warrant or Right [Line Items]
Other (income) expense, net		$ (462)	$ 3,423	$ (1,773)	$ 3,845
Cost of warrant exercised	$ 1,200
Number of shares surrendered (in shares)	64,646
Number of shares issued resulting from exercise (in shares)	333,685
Redeemable Convertible Preferred Stock Warrant Liability
Class of Warrant or Right [Line Items]
Other (income) expense, net			$ 3,200		$ 3,600
Redeemable Convertible Preferred Stock Warrants | Series A-1 Redeemable Convertible Preferred Stock
Class of Warrant or Right [Line Items]
Number of shares issued upon exercisable of warrants (in shares)		124,506		124,506
Exercise price of warrants (in dollars per share)		$ 3.13		$ 3.13
Redeemable Convertible Preferred Stock Warrants | Series A-2 Redeemable Convertible Preferred Stock
Class of Warrant or Right [Line Items]
Number of shares issued upon exercisable of warrants (in shares)		273,825		273,825