Redeemable Convertible Preferred Stock Warrants (Details) - USD ($)	1 Months Ended			12 Months Ended
	May 31, 2018	Mar. 31, 2018	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Class of Warrant or Right [Line Items]
Proceeds from term loans				$ 0	$ 118,578,000	$ 30,000,000
Exercise price of Series G redeemable convertible preferred stock warrants (in dollars per share)	$ 16.3836
Expiration period	10 years
Change in fair value of redeemable convertible preferred stock warrant liability				$ 0	$ 9,591,000	$ 2,200,000
Line of Credit | Term Loan | First WTI Facility due February 2022
Class of Warrant or Right [Line Items]
Proceeds from term loans			$ 30,000,000.0
Line of Credit | Term Loan | First WTI Facility due September 2022
Class of Warrant or Right [Line Items]
Proceeds from term loans		$ 30,000,000.0
June 2017 Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Outstanding warrants to purchase Series G redeemable preferred stock (in shares)							411,991
September 2017 Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Outstanding warrants to purchase Series G redeemable preferred stock (in shares)			205,995
March 2018 Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Outstanding warrants to purchase Series G redeemable preferred stock (in shares)		205,995
May 2018 Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Outstanding warrants to purchase Series G redeemable preferred stock (in shares)	109,288