Subsequent events (Details Textual)	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Percentage Of Change in Price Per Gallon	13.00%	13.00%

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