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	$ 473	$ 296	$ 771	$ 488
Other Nonoperating Income	0	1	2	0
Other Nonoperating Expense	(1)	0	0	0
Insurance policy expense	(11)	(12)	(35)	(36)
Defined Benefit Plan, Non-service Costs	(1,487)	(749)	(3,250)	(2,247)
Other expense, net	$ (1,026)	$ (464)	$ (2,512)	$ (1,795)