Net Loss Per Share Attributable to Common Shareholders - Weighted-Average Common Stock Equivalents were Excluded From Calculation of Diluted Net Loss Per Share Attributable to Common Shareholders (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	63,377,132	107,597,400	101,230,264
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	46,104,469	92,783,867	88,473,431
Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	17,183,546	14,701,626	12,644,926
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	4,952
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	55,961	55,032	55,032
Convertible Preferred Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	28,204	56,875	56,875