Pension benefits (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 368	$ 477	$ 491
Interest cost	170	219	222
Actuarial loss (gain) recognized	(315)	(79)	4
Net periodic pension cost	$ 223	$ 617	$ 717