Commitments and Contingencies - Additional Information (Details) € in Thousands		1 Months Ended	12 Months Ended
	Feb. 10, 2016	Jul. 31, 2010 USD ($) shares	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)
Commitments And Contingencies [Line Items]
Milestone payment		$ 4,700,000.0
Common stock, shares issued (in shares) | shares		105,000
License agreement, termination period	60 days
University of Zurich
Commitments And Contingencies [Line Items]
Percentage of royalty on net product sales (as a percent)			4.00%	4.00%
Percentage requiring reduction in the amount of royalties owned (as a percent)			10.00%	10.00%
Minimum percentage of royalty on net product sales (as a percent)			2.00%	2.00%
University of Zurich | Clinical Development Milestone
Commitments And Contingencies [Line Items]
Amount payable upon achievement of first milestone				$ 750,000
Micromet AG
Commitments And Contingencies [Line Items]
Milestone payment | €			€ 3,600
Percentage of royalty on net product sales (as a percent)			3.50%	3.50%
License agreement, royalty payment, reduction, conditions not met, percent			1.50%	1.50%
License maintenance fees | €			€ 50
XOMA
Commitments And Contingencies [Line Items]
Amount payable upon achievement of first milestone				$ 250,000
Percentage of royalty on net product sales (as a percent)			2.50%	2.50%
Percentage requiring reduction in the amount of royalties owned (as a percent)			50.00%	50.00%
Minimum percentage of royalty on net product sales (as a percent)			1.75%	1.75%
Merck KGaA
Commitments And Contingencies [Line Items]
Amount payable upon achievement of first milestone				$ 4,000,000
Percentage of royalty on net product sales (as a percent)			1.50%	1.50%
License agreement, amount payable upon start of the first phase 3 clinical trial for licensed product				$ 2,000,000
License agreement, amount payable upon submission of the first biologics license application (BLA) for a licensed product				2,000,000
License agreement, amount payable upon the approval of the first BLA in certain countries for a licensed product				2,000,000
License agreement, amount payable upon each of the second and third approvals of a BLA in certain additional countries for the same licensed product				1,000,000
License agreement, amount payable upon the approval of the second BLA in certain countries for a licensed product				2,000,000
License agreement, amount payable upon each of the second and third approvals of the second BLA in certain additional countries for the same licensed product				1,000,000
License agreement, royalty payable on net product sales, maximum amount				$ 150,000,000
Period of expiration of first commercial sale of a licensed product			10 years	10 years
Maximum period of duration of non-payment of royalty of a licensed product			15 years	15 years
Clinical Development
Commitments And Contingencies [Line Items]
Milestone payment upon achievement of clinical milestone					$ 350,000