Leases - Leases (Details) - Office and Laboratory Space in Needham, Massachusetts $ in Millions	Feb. 15, 2018 USD ($) ft²	Apr. 15, 2014 ft²
Leases
Area of space \| ft²	27,810	15,197
Minimum
Leases
Operating lease expense	$ 0.7
Maximum
Leases
Operating lease expense	$ 1.1

Amount of operating lease expense. Excludes sublease income.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918638-209977

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