Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 42,284	$ 42,612
United States
Disaggregation of Revenue [Line Items]
Revenue	29,375	30,889
Total International
Disaggregation of Revenue [Line Items]
Revenue	12,909	11,723
Implant-based
Disaggregation of Revenue [Line Items]
Revenue	34,412	35,290
Implant-based | United States
Disaggregation of Revenue [Line Items]
Revenue	28,870	30,512
Implant-based | Total International
Disaggregation of Revenue [Line Items]
Revenue	5,542	4,778
Shipment-based
Disaggregation of Revenue [Line Items]
Revenue	7,872	7,322
Shipment-based | United States
Disaggregation of Revenue [Line Items]
Revenue	505	377
Shipment-based | Total International
Disaggregation of Revenue [Line Items]
Revenue	$ 7,367	$ 6,945