Nature of the business and basis of presentation (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 06, 2019	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Subsidiary, Sale of Stock
Common stock issued (in shares) | shares			28,567,837	238,986
Proceeds received, net of underwriting discounts and commissions			$ 85
Offering costs				$ 449
Authorized common stock (in shares) | shares			150,000,000	75,000,000
Par value common stock (in dollars per share) | $ / shares			$ 0.0001	$ 0.0001
Reverse stock split of the common stock		3.07418
Net loss			$ 43,755	$ 81,714
Accumulated deficit			130,320	$ 86,565
Cash, cash equivalents and short-term marketable securities			$ 136,400
IPO
Subsidiary, Sale of Stock
Common stock issued (in shares) | shares	6,612,500
Public offering price (in dollars per share) | $ / shares	$ 16.00
Proceeds received, net of underwriting discounts and commissions	$ 98,394
Offering costs	$ 2,942
Conversion of convertible preferred stock into common stock | shares	21,056,136
Authorized common stock (in shares) | shares	150,000,000
Par value common stock (in dollars per share) | $ / shares	$ 0.0001
Authorized Preferred stock (in shares) | shares	10,000,000
Par value preferred stock (in dollars per share) | $ / shares	$ 0.0001
Over allotment
Subsidiary, Sale of Stock
Proceeds received, net of underwriting discounts and commissions	$ 98,394
Over allotment | Maximum
Subsidiary, Sale of Stock
Common stock issued (in shares) | shares	862,500