Subsequent events (Details Textual) - February 2018 Public Offering [Member] - Pre-funded Warrants [Member] - shares		3 Months Ended
Apr. 19, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Warrants exercised		178,078
Subsequent Event [Member]
Subsequent Event [Line Items]
Warrants exercised	851,155

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

No definition available.

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration