Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Data (Unaudited)
Total revenue	$ 7,064	$ 7,164	$ 6,659	$ 6,207	$ 6,800	$ 7,092	$ 6,349	$ 6,305	$ 27,094	$ 26,546	$ 24,896
Gross profit	3,232	4,305	3,500	3,662	2,921	3,634	3,631	3,792	14,699	13,978	13,090
Net loss	$ (5,308)	$ (1,444)	$ (5,416)	$ (4,540)	$ (6,253)	$ (4,509)	$ (3,268)	$ (4,153)	$ (16,708)	$ (18,183)	$ (10,183)
Net loss per common share, basic and diluted	$ (0.48)	$ (0.54)	$ (2.12)	$ (1.78)	$ (2.45)	$ (1.77)	$ (1.28)	$ (1.63)	$ (3.53)	$ (7.12)	$ (4.00)