Significant agreements - AstraZeneca Collaboration Agreement (Details)	1 Months Ended					3 Months Ended		9 Months Ended
	May 31, 2019 employee	May 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Aug. 31, 2017	Nov. 30, 2016 USD ($) employee item	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)
Significant agreements.
Collaboration revenues						$ 3,842,000	$ 614,000	$ 6,542,000	$ 8,520,000
Deferred revenue						33,275,000		33,275,000		$ 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						213,000	441,000	944,000	1,229,000
Deferred revenue						5,090,000		5,090,000		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						200,000	400,000	900,000	1,000,000
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		0
AstraZeneca | 2016 Collaboration Agreement | Target One and Target Two Research License and Related Services
Significant agreements.
Collaboration revenues						0	$ 0	0	$ 200,000
AstraZeneca | May 2018 Option Exercise
Significant agreements.
Biological Targets | item					4
Option fee for development and exploitation rights		5,000,000	$ 5,000,000		$ 5,000,000
Number of FTE | employee	2
Customer option payment		$ 8,000,000
Transaction price						5,650,000		5,650,000			$ 6,300,000
Deferred revenue						5,100,000		5,100,000		$ 4,900,000
AstraZeneca | May 2018 Option Exercise | Target Three Research License and Related Services
Significant agreements.
Transaction price						650,000		650,000
AstraZeneca | May 2018 Option Exercise | Target 3 Material Right
Significant agreements.
Transaction price						1,504,000		1,504,000
AstraZeneca | May 2018 Option Exercise | Target 4 Material Right
Significant agreements.
Transaction price						1,204,000		1,204,000
AstraZeneca | May 2018 Option Exercise | Target 5 Material Right
Significant agreements.
Transaction price						1,165,000		1,165,000
AstraZeneca | May 2018 Option Exercise | Target 6 Material Right
Significant agreements.
Transaction price						$ 1,127,000		$ 1,127,000