License Agreements - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Nov. 30, 2017	Feb. 01, 2016	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
License Agreements [Line Items]
Research and development expense			$ 7,781,000	$ 3,190,000	$ 13,502,000	$ 5,425,000
Duke University
License Agreements [Line Items]
Sublicensable agreement expiration, year		2029
Sale of licensed products or services					0
Fees payment					300,000
Nonroyalty payment received					$ 1,000,000
Nonroyalty agreement term					The Company must pay Duke the first $1.0 million of non-royalty payments it receives from a sublicensee, and thereafter a specified percentage of any additional nonroyalty payments it receives, subject to certain conditions. If Duke receives revenue as a result of a license or sublicense to a third-party in the field of small-molecule oncologics, it will pay the Company a specified percentage of the amount of such revenue in excess of $0.1 million.
Wacker
License Agreements [Line Items]
Research and development expense			0
Maximum | Achievement Of Clinical Development And Regulatory Milestones | Duke University
License Agreements [Line Items]
Potential milestones payment					$ 2,200,000
Maximum | Commercial Milestones | Duke University
License Agreements [Line Items]
Potential milestones payment					400,000
Minimum | Duke University
License Agreements [Line Items]
Aggregate royalties payment					$ 200,000
MedImmune Limited
License Agreements [Line Items]
License agreement upfront payment	$ 100,000
Research and development expense			$ 1,000,000
Reimbursement of costs incurred to product storage costs							$ 500,000
MedImmune Limited | Maximum | Achievement Of Clinical Development And Regulatory Milestones
License Agreements [Line Items]
Potential milestones payment	18,000,000
MedImmune Limited | Maximum | Commercial Milestones
License Agreements [Line Items]
Potential milestones payment	$ 50,000,000