Summary of significant accounting policies - Property and equipment (Details)	3 Months Ended
	Mar. 31, 2020
Leasehold improvements
Property and equipment
Estimated useful life	5 years
Laboratory equipment | Minimum
Property and equipment
Estimated useful life	3 years
Laboratory equipment | Maximum
Property and equipment
Estimated useful life	10 years
Furniture and fixtures | Minimum
Property and equipment
Estimated useful life	3 years
Furniture and fixtures | Maximum
Property and equipment
Estimated useful life	10 years
Computer equipment and software | Minimum
Property and equipment
Estimated useful life	3 years
Computer equipment and software | Maximum
Property and equipment
Estimated useful life	4 years