Pension - Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Components of net periodic benefit cost:
Interest cost	$ 14	$ 14	$ 28	$ 28
Service cost	9	9	18	18
Expected return on plan assets	(20)	(19)	(40)	(38)
Amortization of prior service costs	2		4
Amortization of actuarial loss	26	31	52	62
Net periodic benefit cost	$ 31	$ 35	$ 62	$ 70