Equity Based Compensation - Stock option awards (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Number of Shares
Outstanding at the beginning	2,987,403
Granted	1,468,885
Exercised	(35,822)
Forfeited	(64,917)
Outstanding at the end	4,355,549	2,987,403
Options vested and expected to vest at the end	4,355,549
Options exercisable at the end	655,162
Weighted Average Exercise Price
Outstanding at the beginning (in dollars per share)	$ 8.67
Granted (in dollars per share)	14.68
Exercised (in dollars per share)	4.67
Forfeited (in dollars per share)	6.24
Outstanding at the end (in dollars per share)	10.77	$ 8.67
Options vested and expected to vest at the end (in dollars per share)	10.77
Options exercisable at the end (in dollars per share)	$ 5.31
Weighted Average Remaining Contractual Term and Aggregate Intrinsic Value
Expected term (in years)	9 years 2 months 9 days	9 years 2 months 19 days
Options vested and expected to vest at the end	9 years 2 months 9 days
Options exercisable at the end (in years)	8 years 3 months 11 days
Outstanding at the beginning (in dollars)	$ 26,254
Outstanding at the end (in dollars)	20,121	$ 26,254
Options vested and expected to vest at the end	20,121
Options exercisable at the end (in dollars)	$ 6,165
Weighted average grant date fair value per share of stock options granted to employees and non-employees for stock option awards	$ 6.37
Stock option
Weighted Average Remaining Contractual Term and Aggregate Intrinsic Value
Unrecognized equity based compensation expense	$ 27,500
Unrecognized equity based compensation expense expected period for recognition	3 years 2 months 12 days
Weighted average grant date fair value per share of stock options granted to employees and non-employees for stock option awards	$ 10.02
2019 Equity Incentive Plan | Stock option
Assumptions used in determining the fair value of the options granted
Risk-free interest rate	0.48%
Expected term (in years)	6 years
Expected volatility	80.85%