Pension - Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Components of net periodic benefit cost:
Service cost	$ 7	$ 9	$ 25	$ 27
Interest cost	10	8	30	36
Expected return on plan assets	(17)	(12)	(51)	(52)
Amortization of prior service costs		(4)
Amortization of actuarial loss	21	29	65	81
Total non-service cost	14	21	44	65
Net periodic pension cost	$ 21	$ 30	$ 69	$ 92