Intangible assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets [Abstract]
Amortization of Intangible Assets	$ 400	$ 100	$ 100
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 875