Income Taxes Interest and Penalty Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Interest expense (benefit)	$ 144	$ 121	$ 15
Penalty expense	$ (64)	$ (29)	$ (98)