Pension Benefits - Component of net periodic benefit cost (Details) - Defined Benefit Pension Items [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of net periodic benefit cost
Service cost	$ 441	$ 374
Interest cost	319	402
Expected return on plan assets	(817)	(762)
Recognized net actuarial loss	648	366
Net periodic pension cost	$ 591	$ 380