Redeemable convertible preferred stock (Details) - USD ($)		1 Months Ended	3 Months Ended
	Apr. 23, 2019	Feb. 28, 2019	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2019
Redeemable convertible preferred stock
Average price (in dollars per sale)				$ 8.25	$ 12.23
Preferred Stock outstanding (in shares)				0
Undesignated Preferred Stock authorized (in shares)				10,000,000
Preferred shares authorized (in shares)			1,580,506
Preferred shares issued and outstanding (in shares)			1,580,506
Carrying value (in dollars per sale)			$ 0.158
Common stock issuable upon conversion (in shares)			18,401,893
IPO
Redeemable convertible preferred stock
Outstanding shares of Preferred Stock converted (in shares)	1,580,506
Amount reclassified upon conversion of Preferred Stock	$ 142,000,000
Common Stock | IPO
Redeemable convertible preferred stock
Average price (in dollars per sale)	$ 14.00
Issuance costs	$ 9,400,000
Stock issued upon conversion of Preferred Stock (in shares)	14,582,161
Series A Preferred Stock
Redeemable convertible preferred stock
Preferred shares authorized (in shares)			137,814
Preferred shares issued and outstanding (in shares)			137,814
Carrying value (in dollars per sale)			$ 0.014
Common stock issuable upon conversion (in shares)			1,604,574
Series B Preferred Stock
Redeemable convertible preferred stock
Preferred shares authorized (in shares)			492,192
Preferred shares issued and outstanding (in shares)			492,192
Carrying value (in dollars per sale)			$ 0.049
Common stock issuable upon conversion (in shares)			5,730,612
Series C Preferred Stock
Redeemable convertible preferred stock
Preferred shares authorized (in shares)			693,500
Preferred shares issued and outstanding (in shares)			693,500
Carrying value (in dollars per sale)			$ 0.069
Common stock issuable upon conversion (in shares)			8,074,447
Series D Preferred Stock
Redeemable convertible preferred stock
Preferred Stock issued (in shares)		257,000
Average price (in dollars per sale)		$ 145.65
Gross Proceeds from issuance of stock		$ 37,400,000
Issuance costs		$ 200,000
Preferred shares authorized (in shares)			257,000
Preferred shares issued and outstanding (in shares)			257,000
Carrying value (in dollars per sale)			$ 0.026
Common stock issuable upon conversion (in shares)			2,992,260
Class A common stock
Redeemable convertible preferred stock
Number of common stock issued upon conversion of each share of Preferred Stock				11.643
Class A common stock | IPO
Redeemable convertible preferred stock
Stock issued upon conversion of Preferred Stock (in shares)	3,819,732