Significant agreements - AstraZeneca Collaboration Agreement (Details)	1 Months Ended				3 Months Ended
	May 31, 2019 employee	May 31, 2018 USD ($)	Aug. 31, 2017	Nov. 30, 2016 USD ($) employee item	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)
Significant agreements.
Collaboration revenues					$ 1,129,000	$ 6,384,000
Deferred revenue					34,253,000		$ 5,657,000		$ 14,635,000
AstraZeneca
Significant agreements.
Biological Targets | item				6
Term (in years)			3 years
Term, Bicycle Research Team (in years)				1 year
Term, AZ Research (in years)				2 years
Number of FTE | employee				2
Collaboration revenues					412,000	425,000
Deferred revenue					4,658,000		4,913,000		$ 4,727,000
AstraZeneca | Development milestone
Significant agreements.
Transaction price		$ 700,000
AstraZeneca | Target One
Significant agreements.
Transaction price										$ 2,000,000
AstraZeneca | Target Two
Significant agreements.
Transaction price				$ 600,000
AstraZeneca | Target Three Research License and Related Services
Significant agreements.
Collaboration revenues					400,000	300,000
AstraZeneca | Commercialization license per candidate
Significant agreements.
Customer option payment				8,000,000
AstraZeneca | Development Milestone | Development milestone
Significant agreements.
Customer option payment				29,000,000
AstraZeneca | Regulatory Milestone | Regulatory milestone
Significant agreements.
Customer option payment				23,000,000
AstraZeneca | Commercial milestone | Commercial milestone
Significant agreements.
Customer option payment				$ 110,000,000
AstraZeneca | Minimum
Significant agreements.
Term extension (in years)				12 months
AstraZeneca | Maximum
Significant agreements.
Term extension (in years)				15 months
AstraZeneca | 2016 Collaboration Agreement
Significant agreements.
Biological Targets | item				2
Option fee for development and exploitation rights				$ 8,000,000
Transaction price				$ 1,200,000
Deferred revenue					0		$ 0
AstraZeneca | 2016 Collaboration Agreement | Target One and Target Two Research License and Related Services
Significant agreements.
Collaboration revenues					0	100,000
AstraZeneca | May 2018 Option Exercise
Significant agreements.
Biological Targets | item				4
Option fee for development and exploitation rights		5,000,000		$ 5,000,000
Number of FTE | employee	2
Customer option payment		$ 8,000,000
Transaction price					5,650,000			$ 6,300,000
Deferred revenue					4,700,000	$ 4,900,000
AstraZeneca | May 2018 Option Exercise | Target Three Research License and Related Services
Significant agreements.
Transaction price					650,000
AstraZeneca | May 2018 Option Exercise | Target 3 Material Right
Significant agreements.
Transaction price					1,504,000
AstraZeneca | May 2018 Option Exercise | Target 4 Material Right
Significant agreements.
Transaction price					1,204,000
AstraZeneca | May 2018 Option Exercise | Target 5 Material Right
Significant agreements.
Transaction price					1,165,000
AstraZeneca | May 2018 Option Exercise | Target 6 Material Right
Significant agreements.
Transaction price					$ 1,127,000