Other Income, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Interest income	$ 716	$ 244	$ 332
Other nonoperating income	325	208	789
Insurance Policy Expense (Income), Net	(195)	22	(228)
Other nonoperating expense	(13)	(13)	(10)
Other income, net	$ 833	$ 461	$ 883