Nature of the Business and Basis of Presentation (Details) $ / shares in Units, $ in Thousands									1 Months Ended	12 Months Ended
	Mar. 01, 2021 USD ($)	Jul. 24, 2020 USD ($) $ / shares shares	May 18, 2020 USD ($) $ / shares shares	Mar. 01, 2019 USD ($) $ / shares shares	Feb. 04, 2019 USD ($) $ / shares shares	Jun. 22, 2018 USD ($) $ / shares shares	May 29, 2018 USD ($) $ / shares shares	May 11, 2018	Jun. 22, 2018 USD ($) $ / shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	May 31, 2018 shares
Nature of the Business and Basis of Presentation
Reverse stock split								2.73235
Liquidity
Accumulated deficit										$ 517,473	$ 356,092
Net losses										161,381	161,867	$ 103,227
Cash used in operations										136,532	158,369	81,012
Cash, cash equivalents and short-term investments										323,482
Class A common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares							5,546,019						5,546,019
Class A1 common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares							12,995,954						12,995,954
Class B common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares							1,070,502						1,070,502
Class B1 common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares							16,057,618						16,057,618
Initial Public Offering
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions, placement agent fees and other offering costs									$ 155,536			155,536
Initial Public Offering | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares							8,477,777
Share price (in dollars per share) | $ / shares							$ 18.00
Gross proceeds from IPO							$ 152,600
Gross proceeds from offering												$ 159,194
Follow-On Public Offering and Private Placement Inclusive of Over-Allotment
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions, placement agent fees and other offering costs	$ 82,988	$ 146,037	$ 74,495	$ 82,988
Follow-On Public Offering and Private Placement | Common Class A and Class A1 common shares
Nature of the Business and Basis of Presentation
Gross proceeds from offering		$ 155,000	$ 79,570		$ 85,000
Follow-On Offering | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares		5,952,381	2,760,000		2,654,984
Share price (in dollars per share) | $ / shares		$ 21.00	$ 18.25		$ 18.26
Gross proceeds from offering										$ 165,725	$ 48,595
Private Placement | Class A1 common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares		1,428,572	1,600,000		2,000,000
Share price (in dollars per share) | $ / shares		$ 21.00	$ 18.25		$ 18.26
Over-allotment | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares				161,126		1,006,425
Share price (in dollars per share) | $ / shares				$ 18.26		$ 18.00			$ 18.00
Gross proceeds from IPO						$ 18,116
Gross proceeds from offering				$ 2,942