Stock Plans (Details 1) - Employee Stock Purchase Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Maximum employee contribution to ESPP	$ 25
Maximum employee contribution to ESPP, percent of base compensation	10.00%
Common Stock Discount Purchase Price	95.00%
Shares Available Under Employee Stock Purchase Plan	4,550,000
Stock Issued During Period, Shares, Employee Stock Purchase Plans	7,734	11,804	11,246
Proceeds from Stock Plans	$ 444	$ 427	$ 403
Number Of Shares Available Under Employee Stock Purchase Plan	277,671