Income taxes - Schedule of Operating Loss Carryovers (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards [Line Items]
Total loss carryovers	$ 2,510
Year Expiring - 2027 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	1,551
Year Expiring - 2028 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	364
Year Expiring - 2029 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	248
Year Expiring - 2030 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	81
Year Expiring - 2031 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	52
Year Expiring - 2032 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	39
Year Expiring - 2033 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	61
Year Expiring - 2034 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	54
Year Expiring - 2035 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	57
Year Expiring - 2036 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	68
Year Expiring - 2037 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	95
Year Expiring - 2038 [Member]
Operating Loss Carryforwards [Line Items]
Total loss carryovers	$ (160)