Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue	$ 36,238	$ 44,740	$ 71,844	$ 87,024
United States
Disaggregation of Revenue [Line Items]
Revenue	24,013	29,986	46,798	59,361
International
Disaggregation of Revenue [Line Items]
Revenue	12,225	14,754	25,046	27,663
Implant-based
Disaggregation of Revenue [Line Items]
Revenue	26,744	34,266	53,013	68,678
Implant-based | United States
Disaggregation of Revenue [Line Items]
Revenue	23,507	28,416	45,969	57,286
Implant-based | International
Disaggregation of Revenue [Line Items]
Revenue	3,237	5,850	7,044	11,392
Shipment-based
Disaggregation of Revenue [Line Items]
Revenue	9,494	10,474	18,831	18,346
Shipment-based | United States
Disaggregation of Revenue [Line Items]
Revenue	506	1,570	829	2,075
Shipment-based | International
Disaggregation of Revenue [Line Items]
Revenue	$ 8,988	$ 8,904	$ 18,002	$ 16,271