Significant agreements - AstraZeneca Collaboration Agreement (Details)	1 Months Ended				3 Months Ended		6 Months Ended
	May 31, 2019 employee	May 31, 2018 USD ($)	Aug. 31, 2017	Nov. 30, 2016 USD ($) employee item	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jul. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2017 USD ($)
Significant agreements
Collaboration revenues					$ 1,522,000	$ 1,661,000	$ 7,906,000	$ 4,469,000
Deferred revenue					10,370,000		10,370,000			$ 14,635,000	$ 14,467,000
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					362,000	391,000	787,000	691,000
Deferred revenue					4,702,000		4,702,000			4,727,000	$ 0
AstraZeneca | Development milestone
Significant agreements
Transaction price		$ 700,000
AstraZeneca | Target One
Significant agreements
Transaction price				$ 600,000								$ 2,000,000
AstraZeneca | Target Two
Significant agreements
Transaction price				600,000
AstraZeneca | Target Three Research License and Related Services
Significant agreements
Collaboration revenues					300,000	100,000	600,000	100,000
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			$ 24,000
AstraZeneca | 2016 Collaboration Agreement | Target One and Target Two Research License and Related Services
Significant agreements
Collaboration revenues					25,000	$ 300,000	200,000	$ 600,000
AstraZeneca | May 2018 Option Exercise
Significant agreements
Biological Targets | item				4
Option fee for development and exploitation rights		5,000,000		$ 5,000,000
Customer option payment		$ 8,000,000
Number of FTE | employee	2
Transaction price					5,650,000		5,650,000		$ 6,300,000
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