Collaboration Agreements (Adicet Bio) (Details) - USD ($) $ in Millions	1 Months Ended
Jul. 31, 2016	Jul. 30, 2016
Collaboration Agreements [Line Items]
Period over which we have obligation		5 years
Adicet Bio [Member]
Collaboration Agreements [Line Items]
Other Research and Development Expense	$ 25.0

Amount of other research and development expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

Name:	us-gaap_OtherResearchAndDevelopmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration