Pension benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Amortization of transition obligation	$ 43	$ 40	$ 39
Actuarial gain (loss)	(179)	986	574
Totals	136	(1,026)	$ (613)
Amounts in accumulated other comprehensive loss not yet reflected in net periodic pension cost, net of taxes:
Actuarial gain	1,557	1,736
Transition obligation	(170)	(213)
Totals	1,387	$ 1,523
Amounts in accumulated other comprehensive loss expected to be amortized in 2017 net periodic pension cost, net of taxes:
Actuarial gain	(286)
Transition obligation	38
Totals	$ (248)