Summary of significant accounting policies - Narrative (Details) (USD $)	10 Months Ended	1 Months Ended
Dec. 31, 2014 segment	Jan. 31, 2015
Entity Location [Line Items]
Number of operating segments	1us-gaap_NumberOfOperatingSegments
IPO issuance cost	$ 1,075,000us-gaap_DeferredOfferingCosts
United States
Entity Location [Line Items]
Number of geographic segments	1
Subsequent Event
Entity Location [Line Items]
Reverse stock split conversion ratio		0.2335

Specific incremental costs directly attributable to a proposed or actual offering of securities which are deferred at the end of the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.8)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 340

-SubTopic 10

-Section S99

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=27011391&loc=d3e105025-122735

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section A

Name:	us-gaap_DeferredOfferingCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant