Significant Agreements - Celgene Collaboration Agreement (Details) $ / shares in Units, $ in Millions	Mar. 20, 2018 USD ($) agreement_term $ / shares shares
Collaboration Program, US Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, potential regulatory milestone payments per program	$ 90.0
Collaboration agreement, potential commercial milestone payments per program	375.0
Collaboration Program, US Rights | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, expected allocation of initial transaction price	15.0
Collaboration Program, US Rights | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, expected allocation of initial transaction price	25.0
Collaboration Program, Global Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, potential regulatory milestone payments per program	187.5
Collaboration agreement, potential commercial milestone payments per program	375.0
Collaboration Program, Global Rights | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, expected allocation of initial transaction price	10.0
Collaboration Program, Global Rights | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, expected allocation of initial transaction price	18.0
Celgene
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, upfront payment	100.0
Collaboration agreement, potential regulatory and commercial milestone payments per program	$ 562.5
Collaboration agreement, term of agreement	6 years
Collaboration agreement, number of additional 12 month period extension allowed | agreement_term	2
Collaboration agreement, extension fee per extension period	$ 10.0
Collaboration agreement, upfront payment, payment term	10 days
Collaboration agreement, option fees and milestone payments, payment term	30 days
Celgene | Collaboration Program, US Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, exercise fee per program	$ 80.0
Celgene | Collaboration Program, Global Rights
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, exercise fee per program	$ 55.0
Celgene | Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Share subscription agreement, number of ordinary shares issued in transaction (in shares) | shares	1,174,536
Share subscription agreement, price per share (in dollars per share) | $ / shares	$ 42.57
Share subscription agreement, consideration received on transaction	$ 50.0
Share subscription agreement, premium received on transaction	10.2
Collaborative Arrangement | Celgene
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, initial transaction price	$ 110.2