Acquisition - Narrative (Details) - USD ($)			1 Months Ended		3 Months Ended		6 Months Ended		22 Months Ended	47 Months Ended
	May 30, 2018	Aug. 24, 2016	Jun. 30, 2019	Aug. 31, 2016	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	May 31, 2018	Jun. 30, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development					$ 53,152,000	$ 51,884,000	$ 104,168,000	$ 89,287,000
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount paid									$ 11,500,000
Upfront option fee				$ 500,000
Contingent consideration payment			$ 1,500,000
Contingent consideration recognized	$ 0				0	1,500,000	0	1,500,000
Research and development					$ 300,000	$ 300,000	$ 600,000	$ 500,000		$ 19,800,000
Maximum development plan period for research costs		24 months
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma | Exercise of buy-out option
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial option exercise payments		$ 17,800,000
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma | Exercise of buy-out option | Preclinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	27,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma | Exercise of buy-out option | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	50,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma | Exercise of buy-out option | Regulatory
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	120,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma | Exercise of buy-out option | Commercial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	250,000,000.0
Collaborative Arrangement with F-Star and Acquisition of F-Star Gamma | Exercise of buy-out option | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent payments upon the achievement of milestones	$ 447,000,000.0