License Agreement with Roche (Details) - USD ($)			3 Months Ended	7 Months Ended
	Jan. 01, 2018	Jun. 10, 2016	Mar. 31, 2019	Dec. 31, 2016
Organization And Basis Of Presentation [Line Items]
Adjustments to transaction price			$ 0
Revenue recognized			$ 0
Roche
Organization And Basis Of Presentation [Line Items]
Up-front license fee				$ 7,500,000
Additional up-front fee		$ 240,000,000
Roche | Collaborative Arrangement, Revenue Based on Development Milestone
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestones		50,000,000
Roche | First Indication
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestones		175,000,000
Roche | Collaborative Arrangement, Revenue Based on Regulatory Milestone
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestones		50,000,000
Roche | Collaborative Arrangement, Revenue Based on Commercialization Milestone
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestones		75,000,000
Roche | Second Indication
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestones		$ 65,000,000
Roche | EBI-031 | Minimum
Organization And Basis Of Presentation [Line Items]
Royalty rate		7.50%
Roche | EBI-031 | Maximum
Organization And Basis Of Presentation [Line Items]
Royalty rate		15.00%
Roche | EBI-031 | Collaborative Arrangement, Revenue Based on Development Milestone
Organization And Basis Of Presentation [Line Items]
Amount payable upon achievement of specified milestones				$ 22,500,000
Roche | IL-6
Organization And Basis Of Presentation [Line Items]
Royalty rate		50.00%
Roche
Organization And Basis Of Presentation [Line Items]
Revenue recognized, transaction price	$ 30,000,000