Revenue Recognition (Details 1) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 2,932	$ 2,933
Deferred revenue, Billings	758	750
Deferred revenue, Revenue Recognized	(1,294)	(1,262)
Deferred revenue, Balance at End of Period	$ 2,396	$ 2,421