Agreements - Gilead (Details) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended
	Dec. 19, 2018 USD ($) item $ / shares shares	Jul. 31, 2019 $ / shares shares	Jun. 30, 2019 $ / shares shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($)
Agreements
Sale of common shares (in shares) | shares		450,000	3,000,000
Purchase price (in dollars per share) | $ / shares		$ 15.00	$ 15.00		$ 15.00
Sale of common shares				$ 6,326	$ 42,022
Revenue received				4,774		$ 12,919
Gilead
Agreements
Number of programs | item	3
Option exercise period	90 days
Upfront payment received	$ 50,000
Potential milestone payments	475,000
Total potential milestone payments	1,425,000
Refundable payments under the agreement	$ 0
Sale of common shares (in shares) | shares	980,392
Purchase price (in dollars per share) | $ / shares	$ 30.60
Sale of common shares	$ 30,000
Maximum number of program antibodies to be notified which satisfies development criteria | item	2
Transaction price	$ 80,000
Research collaboration term	3 years
Equity investment included in transaction price	$ 17,100
Contract liability	62,900
Securities premium				12,900		12,900
Revenue received				$ 4,800		$ 12,900
Gilead | Development milestones
Agreements
Potential milestone payments	$ 25,000