Income Taxes Interest and penalties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accrued interest and penalties (tax) [Abstract]
Income Tax Examination, Penalties and Interest Expense	$ 67	$ 40	$ 78
Income Tax Examination, Penalties and Interest Accrued	$ 564	$ 545	$ 468