Significant accounting policies Reclassification (Details)	12 Months Ended
Jan. 31, 2018 USD ($)
Reclassification from short-term to long-term	$ 2,000,000

The amount of a reclassification adjustment made to prior period financial statement amounts.

No definition available.

Name:	us-gaap_PriorPeriodReclassificationAdjustment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration