Equity Incentive Plan - Stock option (Details) - 2019 Equity Incentive Plan	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Number of Shares
Balance at beginning of period (in shares) | shares	3,742,144
Granted (in shares) | shares	1,446,250
Exercised (in shares) | shares	(223,143)
Cancelled (in shares) | shares	(44,394)
Balance at end of period (in shares) | shares	4,920,857	3,742,144
Vested and expected to vest at end of period (in shares) | shares	4,920,857
Exercisable at end of period (in shares) | shares	2,312,537
Vested at end of period (in shares) | shares	1,916,554
Weighted-Average Exercise Price
Balance at beginning of period (in dollars per share) | $ / shares	$ 9.58
Granted (in dollars per share) | $ / shares	21.33
Exercised (in dollars per share) | $ / shares	5.07
Cancelled (in dollars per share) | $ / shares	15.63
Balance at end of period (in dollars per share) | $ / shares	13.18	$ 9.58
Vested and expected to vest at end of period (in dollars per share) | $ / shares	13.18
Exercisable at end of period (in dollars per share) | $ / shares	9.07
Vested at end of period (in dollars per share) | $ / shares	$ 9.88
Weighted-Average Remaining Contractual Life
Weighted-Average Remaining Contractual Life	8 years 3 months 18 days	8 years 7 months 6 days
Vested and expected to vest at end of period (in years)	8 years 3 months 18 days
Exercisable at end of period (in years)	7 years 7 months 6 days
Vested at end of period (in years)	7 years 8 months 12 days
Aggregate Intrinsic Value
Balance at beginning of period | $	$ 22,910
Balance at end of period | $	16,009	$ 22,910
Vested and expected to vest at end of period | $	16,009
Exercisable at end of period | $	13,441
Vested at end of period | $	$ 9,948