Stock-Based Compensation - Stock options (Details) - USD ($)		1 Months Ended	12 Months Ended
	May 03, 2019	May 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Based Compensation
Antidilutive securities excluded from computation of diluted net loss per share			2,170,212	17,617,460
2015 Plan
Number of Shares
Outstanding at the beginning (in shares)			2,056,891	506,586
Granted (in shares)			258,897	1,570,136
Exercised			(125,108)	(5,599)
Forfeitures			(20,468)	(14,232)
Outstanding at the end (in shares)			2,170,212	2,056,891	506,586
Vested and expected to vest at the end (in shares)			2,170,212
Exercisable at the end (in shares)			716,393
Weighted Average Exercise Price
Outstanding at the beginning (in dollars per share)			$ 4.74	$ 0.94
Granted (in dollars per share)			18.88	5.92
Exercised (in dollars per share)			0.96	0.84
Forfeitures (in dollars per share)			19.66	1.11
Outstanding at the end (in dollars per share)			6.51	$ 4.74	$ 0.94
Vested and expected to vest at the end (in dollars per share)			6.51
Exercisable at the end (in dollars per share)			$ 3.75
Weighted Average Remaining Contractual Life (Years) And Aggregate Intrinsic Value
Outstanding (in years)			8 years 7 months 6 days	9 years 4 months 24 days	9 years
Granted (in years)			9 years 6 months	9 years 10 months 24 days
Exercised (in years)			7 years 4 months 24 days
Forfeitures (in years)			9 years 6 months
Outstanding at the beginning (in dollars)			$ 5,946,000	$ 137,000
Outstanding at the end (in dollars)				$ 5,946,000	$ 137,000
Vested and expected to vest at the end (in dollars)			113,295,000
Exercisable at the end (in dollars)			$ 39,370,000
Weighted average grant date fair value per share of stock options granted			$ 11.92	$ 3.80
Aggregate intrinsic value of stock options exercised			$ 7,225,000	$ 38,000
Aggregate grant date fair value			$ 7,637,000	$ 157,000
2015 Plan | Restricted Common Stock
Stock Based Compensation
Number of shares issued		62,237
Vesting period		4 years
Omnibus Incentive Plan
Stock Based Compensation
Number of shares reserved for issuance under the plan	2,900,000
Annual increase in number of share reserved for issuance (as percent)	4.00%
2015 Plan and 2019 Employee Stock Purchase Plan
Stock Based Compensation
Vesting period			4 years
Expiration period			10 years
Number of shares reserved for issuance under the plan			2,661,566
2019 Employee Stock Purchase Plan
Stock Based Compensation
Number of shares issued			0
Number of shares reserved for issuance under the plan	240,000		240,000
Annual increase in number of share reserved for issuance (as percent)	1.00%
Maximum annual increase in shares available for issuance under the plan	480,000
Option to purchase common stock
Stock Based Compensation
Antidilutive securities excluded from computation of diluted net loss per share			2,170,212	2,056,891