Intangible assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Changes in intangible assets
Finite-Lived Intangible Assets, Net, Beginning Balance	$ 19,676	$ 23,413
Amortization expense	(3,594)	(3,682)
Impairment loss	(27)	(55)
Finite-Lived Intangible Assets, Net, Ending Balance	$ 16,055	$ 19,676