Other Income, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Interest income	$ 271	$ 138	$ 412	$ 342
Other nonoperating income	8	8	56	238
Other nonoperating expense	(4)	(3)	(11)	(10)
Insurance policy income (expense)	166	(48)	72	(146)
Defined Benefit Plan, Non-service Costs	(1,223)	(678)	(2,180)	(2,034)
Other expense, net	$ (782)	$ (583)	$ (1,651)	$ (1,610)