Summary of Significant Accounting Policies - Subsequent Events (Details) - IMGN779 [Member] - Subsequent event - Jazz Pharmaceuticals $ in Millions	3 Months Ended
Dec. 31, 2019 USD ($)
Subsequent Event [Line Items]
Revenue to be recognized	$ 14.5
Deferred revenue	$ 75.0

Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(5))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DeferredRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant