Commitments and Contingencies - Leases, Tenancy agreement (Details) - Tenancy agreement for space in Building 260 Babraham Research Campus, Cambridge - USD ($) $ in Millions	Oct. 31, 2017	Sep. 30, 2015
Leases
Leases, term of contract		2 years
Annual rent	$ 0.2	$ 0.2

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant