Related party transactions (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($) item	Sep. 30, 2019 USD ($) item	Sep. 30, 2018 USD ($) item
Investor \| Consulting and management services
Related party transactions
Number of individuals providing services	1	1	1	1
Former Executives \| Board and scientific advisory services
Related party transactions
Number of individuals providing services	2		2
Total amount of services received \| $	$ 100,000.0	$ 33,000.0	$ 200,000.0	$ 84,000.0

Amount of transactions with related party during the financial reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

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