Other Income (Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Interest and investment income	$ 238	$ 548	$ 72
Income tax expense	(327)	(214)	(566)
Other non-operating income	4	0	126
Total other income (expense)	$ (85)	$ 334	$ (368)