Property and equipment (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property And Equipment Narrative Details
Depreciation expense	$ 1,141	$ 1,120	$ 429
Property and equipment under capital lease	704	704
Accumulated depreciation related to assets under capital lease	$ 704	$ 704