License, Acquisition and Collaboration Agreements - Primatope Stock Purchase Option Agreement (Details) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($)	Sep. 30, 2017 USD ($) item	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
License and Acquisition Agreements
Research and development			$ 22,324	$ 30,848	$ 43,225	$ 90,101
Primatope | Stock Option Purchase Agreement
License and Acquisition Agreements
Percentage of capital stock available to purchase in call option		100.00%
Payment for extension of option period							$ 800
Primatope Acquisition
License and Acquisition Agreements
Purchase price	$ 15,000
Upfront consideration payable on exercise of call option to acquire all outstanding equity	10,000
Milestone payment payable after achievement of specified milestones	$ 5,000			$ 3,000		3,000
Research and development						$ 18,000
Primatope Acquisition | Stock Option Purchase Agreement
License and Acquisition Agreements
Upfront payment for initial option period		$ 500
Maximum | Primatope | Stock Option Purchase Agreement
License and Acquisition Agreements
Number of extensions allowed for initial option period | item		3
Total aggregate extension payments		$ 800