Share Based Award ESPP Table (Details) - Employee Stock [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Employee Stock Purchase Plans	23,426	31,227	34,299
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 986	$ 955	$ 1,382
Fair Value Assumptions, Expected Term	6 months	6 months	6 months
Expected stock price volatility	28.10%	32.50%	27.00%
Risk-Free Interest Rate	0.60%	0.30%	0.60%
Expected Dividend Yield	0.00%	0.00%	0.00%