Stock-Based Compensation - Stock options activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended	12 Months Ended
	Apr. 16, 2019	Jun. 30, 2020	Dec. 31, 2019
Common stock reserved for future issuance
Expiry period	10 years
Number of shares
Outstanding at beginning of period (in shares)		1,046,373
Options granted (in shares)		40,993
Options exercised (in shares)		(72,394)
Options canceled (in shares)		(6,065)
Outstanding at end of period (in shares)		1,008,907	1,046,373
Vested and Exercisable (in shares)		374,127
Weighted-average exercise price
Outstanding price at beginning (per share)		$ 17.05
Options granted (per share)		58.79
Options exercised (per share)		15.04
Options canceled (per share)		41.07
Outstanding price at ending (per share)		18.75	$ 17.05
Vested and Exercisable (per share)		$ 15.06
Additional disclosures
Weighted average remaining contractual term for outstanding options (in years)		8 years 10 months 10 days	9 years 3 months 29 days
Weighted average remaining contractual term for Vested and Exercisable options (in years)		8 years 9 months 7 days
Aggregate intrinsic value		$ 67,610	$ 35,039
Aggregate intrinsic value		26,450
Total unrecognized stock-based compensation expense		$ 2,900
Weighted-average period over which unrecognized stock-based compensation expense is expected to be recognized		2 years 2 months 5 days
Minimum
Common stock reserved for future issuance
Vesting period	2 years
Vesting percentage on the first anniversary of the grant date	25.00%
Maximum
Common stock reserved for future issuance
Vesting period	4 years
Vesting percentage on the first anniversary of the grant date	50.00%
2019 Equity Incentive Plan
Number of shares
Outstanding at end of period (in shares)		1,008,907