BeiGene Agreement - Narrative (Details) - Collaboration and License Agreement - USD ($)		3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 07, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front fee received	$ 10,000,000.0
Termination of contract, period after first commercial sale of product	10 years
Period required for notice of termination of contract	60 days
Revenue from performance obligations satisfied during reporting period				$ 156,000
Revenue from performance obligation expected to be earned	$ 123,000,000.0
Licenses of Intellectual Property
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned		$ 0		0		$ 9,500,000
Manufacturing Supply Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments received in advance		(600,000)	$ 0	(1,800,000)	$ 0
Revenue from performance obligations satisfied during reporting period				200,000
Revenue from performance obligation earned				1,600,000		$ 500,000
Cost-sharing receivable				500,000
Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation expected to be earned		5,000,000.0		5,000,000.0
Milestone payments earned		0	0	0	0
Royalties
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue		$ 0	$ 0	$ 0	$ 0