Research and Collaboration Agreements - ImmunoGen, Inc - Additional Information (Details) - Collaborative Arrangement - Immuno Gen Inc	1 Months Ended
	Jan. 31, 2014 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated total fair value consideration recorded as deferred revenue	$ 13,200,000
Estimated fair value of assets and services	13,200,000
Licenses Received
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fair value of assets and services	12,700,000
Research Services, Joint Research Committee Participation and Technology Improvements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fair value of assets and services	500,000
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments receivable upon achieving development and regulatory milestones	30,000,000
Contingent payments receivable upon achieving sales milestones	50,000,000
Contingent payments payable upon achieving development and regulatory milestones	60,000,000
Contingent payments payable upon achieving sales milestones	100,000,000
Up Front Payment Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment	0
Research License, Research Services, Joint Research Committee, Commercialization License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated total fair value consideration recorded as deferred revenue	13,000,000
Technology Improvements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated total fair value consideration recorded as deferred revenue	$ 200,000