Pension - Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of net periodic benefit cost:
Interest cost	$ 8	$ 15	$ 36	$ 44
Service cost	9	6	27	19
Expected return on plan assets	(12)	(23)	(52)	(69)
Amortization of prior service costs	(4)	2	0	7
Amortization of actuarial loss	29	28	81	84
Net periodic benefit cost	$ 30	$ 28	$ 92	$ 85