Intangible assets Future intangible amortization schedule (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Future intangible amortization schedule [Abstract]
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 875
Finite-Lived Intangible Assets, Amortization Expense, Year Two	1,111
Finite-Lived Intangible Assets, Amortization Expense, Year Three	1,254
Finite-Lived Intangible Assets, Amortization Expense, Year Four	1,363
Finite-Lived Intangible Assets, Amortization Expense, Year Five	1,154
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	6,056
Finite-Lived Intangible Assets, Net	$ 11,813	$ 844