Collaboration and License Agreement - Narrative (Details) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 02, 2019 USD ($) target product	Jan. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment paid			$ 2,200	$ 0	$ 58,200	$ 0
Codiak Biosciences Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of targets/programs | target	5
Number of projects subject to right to co-commercialize | product	2
Upfront Payment | Codiak Biosciences Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment paid		$ 56,000
Preclinical Development Milestone Payment | Codiak Biosciences Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments per target not yet due or paid	$ 20,000
Milestone Payment | Codiak Biosciences Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone payments per target not yet due or paid	$ 200,000