Stockholder's equity (Details)		1 Months Ended				3 Months Ended
	Sep. 27, 2019 USD ($) $ / shares shares	Nov. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Jul. 31, 2017 USD ($) $ / shares shares	Nov. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2021 USD ($) Vote $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Class of Stock [Line Items]
Preferred stock redemption notice period						180 days
Series B Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares						13,715,330	13,715,330
Preferred stock, par value | $ / shares						$ 0.00001	$ 0.00001
Stock issued during period | shares				13,715,330
Shares Issued, Price Per Share | $ / shares				$ 0.6562		0.6562
Proceeds from issuance of redeemable preferred stock, net of issuance costs | $				$ 8,943,000
Preferred stock conversion price | $ / shares						$ 15,289
Preferred stock, preference in liquidation | $						$ 11,680,000	$ 11,500,000
Series C Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares						26,732,361	26,732,361
Preferred stock, par value | $ / shares						$ 0.00001	$ 0.00001
Stock issued during period | shares		1,048,328	25,684,033
Shares Issued, Price Per Share | $ / shares		$ 0.9539	$ 0.9539			0.9539
Proceeds from issuance of redeemable preferred stock, net of issuance costs | $		$ 25,437,000	$ 25,437,000
Preferred stock conversion price | $ / shares						$ 2.2226
Preferred stock, preference in liquidation | $						$ 30,617,000	$ 30,107,000
Series D Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares						16,758,996	16,758,996
Preferred stock, par value | $ / shares						$ 0.00001	$ 0.00001
Stock issued during period | shares	16,390,217
Shares Issued, Price Per Share | $ / shares	$ 1.5253					1.5253
Proceeds from issuance of redeemable preferred stock, net of issuance costs | $	$ 24,824,000
Preferred stock conversion price | $ / shares						$ 3.5539
Preferred stock, preference in liquidation | $						$ 28,000,000	$ 27,500,000
Class A Common Stock
Class of Stock [Line Items]
Common stock, shares authorized | shares						62,220,020	62,220,020
Common stock, par value | $ / shares						$ 0.00001	$ 0.00001
Common stock, shares issued | shares						0	0
Common stock, shares outstanding | $						$ 0	$ 0
Proceeds from issuance of redeemable preferred stock, net of issuance costs | $						$ 50,000
Preferred stock, automatic conversion trigger, IPO minimum price | $ / shares						$ 3.05
Class B Common Stock
Class of Stock [Line Items]
Common stock, shares authorized | shares						16,822,202	16,822,202
Common stock, par value | $ / shares						$ 0.00001	$ 0.00001
Common stock, shares issued | shares						2,835,099	2,563,765
Common stock, shares outstanding | $						$ 2,835,099	$ 2,563,765
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares						5,013,333	5,013,333
Preferred stock, par value | $ / shares						$ 0.00001	$ 0.00001
Stock issued during period | shares					5,013,333
Shares Issued, Price Per Share | $ / shares					$ 0.25	0.25
Proceeds from issuance of preferred stock | $					$ 1,253,000
Preferred stock conversion price | $ / shares						$ 0.5825
Preferred stock, preference in liquidation | $						$ 1,253,000	$ 1,253,000
Common Stock
Class of Stock [Line Items]
Common stock, shares authorized | shares						79,042,222
Common stock, par value | $ / shares						$ 0.00001
Common Stock | Series B Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock conversion price | $ / shares						0.6562
Common Stock | Series C Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock conversion price | $ / shares						0.9539
Common Stock | Series D Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock conversion price | $ / shares						$ 1.5253
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Common stock, shares authorized | shares						62,220,020
Common Stock Voting Rights Per Share | Vote						1
Common stock, shares issued | shares						0	0
Common Stock, Shares, Outstanding | shares						0	0
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Common stock, shares authorized | shares						16,822,202
Common stock, shares issued | shares						2,835,099	2,563,765
Common Stock, Shares, Outstanding | shares						2,835,099	2,563,765
Common stock, shares reserved for issuance upon the exercise of stock options | shares						5,457,669	4,932,952
Common Stock | Series A Convertible Preferred Stock
Class of Stock [Line Items]
Preferred stock conversion price | $ / shares						$ 0.25
Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares						62,220,020
Preferred stock, par value | $ / shares						$ 0.00001
Dividend accrual rate per annum						8.00%
Preferred Stock | Class A Common Stock
Class of Stock [Line Items]
Common Stock Voting Rights Per Share | Vote						1