Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 35,775	$ 34,756	$ 107,619	$ 121,780
United States
Disaggregation of Revenue [Line Items]
Revenue	24,118	25,699	70,915	85,060
International
Disaggregation of Revenue [Line Items]
Revenue	11,657	9,057	36,704	36,720
Implant-based
Disaggregation of Revenue [Line Items]
Revenue	26,571	30,070	79,584	98,748
Implant-based | United States
Disaggregation of Revenue [Line Items]
Revenue	23,457	25,194	69,425	82,480
Implant-based | International
Disaggregation of Revenue [Line Items]
Revenue	3,114	4,876	10,159	16,268
Shipment-based
Disaggregation of Revenue [Line Items]
Revenue	9,204	4,686	28,035	23,032
Shipment-based | United States
Disaggregation of Revenue [Line Items]
Revenue	661	505	1,490	2,580
Shipment-based | International
Disaggregation of Revenue [Line Items]
Revenue	$ 8,543	$ 4,181	$ 26,545	$ 20,452