Collaboration and Licensing Agreements (Details) - Gilead Collaboration and License Agreement $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($) item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Collaboration and Licensing Agreements
Number of preclinical research programs | item	2
Non-refundable, upfront payment	$ 10.0
Upfront payment recorded as revenue		$ 4.4	$ 2.8
Liability in deferred revenues		2.6
Prepayment received related to ordered manufacturing services		$ 1.0
Percentage of upfront payment included in deferred revenue expected to be recognized in 2020		97.00%
Percentage of upfront payment included in deferred revenue expected to be recognized in 2021		3.00%
Payment term (in days)		60 days
Revenue recognized from cost reimbursements		$ 4.3
Revenue recognized from milestone payments		3.2	2.0
Contract asset relating to the sublicense payment		0.4	0.3
Contract liability relating to sublicense payment			0.5
Development Milestones
Collaboration and Licensing Agreements
Total milestone amount		280.0
Commercial Milestones
Collaboration and Licensing Agreements
Total milestone amount		$ 100.0
Pre-clinical milestone
Collaboration and Licensing Agreements
Revenue recognized from milestone payments			$ 2.8