Income Taxes Unrecognized Tax Benefits Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 900	$ 800	$ 800
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1	974	1,022	1,067
Additions based on tax positions related to the current year	183	160	163
Additions based on tax positions taken in prior years	227	0	0
Decreases based on the expiration of statute of limitations	(359)	(208)	(208)
Balance at December 31	$ 1,025	$ 974	$ 1,022