Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 35,606	$ 42,284
United States
Disaggregation of Revenue [Line Items]
Revenue	22,786	29,375
International
Disaggregation of Revenue [Line Items]
Revenue	12,820	12,909
Implant-based
Disaggregation of Revenue [Line Items]
Revenue	26,270	34,412
Implant-based | United States
Disaggregation of Revenue [Line Items]
Revenue	22,463	28,870
Implant-based | International
Disaggregation of Revenue [Line Items]
Revenue	3,807	5,542
Shipment-based
Disaggregation of Revenue [Line Items]
Revenue	9,336	7,872
Shipment-based | United States
Disaggregation of Revenue [Line Items]
Revenue	323	505
Shipment-based | International
Disaggregation of Revenue [Line Items]
Revenue	$ 9,013	$ 7,367