Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 44,740	$ 48,556	$ 87,024	$ 91,168
United States
Disaggregation of Revenue [Line Items]
Revenue	29,986	31,906	59,361	62,795
International
Disaggregation of Revenue [Line Items]
Revenue	14,754	16,650	27,663	28,373
Implant-based
Disaggregation of Revenue [Line Items]
Revenue	34,266	37,407	68,678	72,697
Implant-based | United States
Disaggregation of Revenue [Line Items]
Revenue	28,416	31,473	57,286	61,985
Implant-based | International
Disaggregation of Revenue [Line Items]
Revenue	5,850	5,934	11,392	10,712
Shipment-based
Disaggregation of Revenue [Line Items]
Revenue	10,474	11,149	18,346	18,471
Shipment-based | United States
Disaggregation of Revenue [Line Items]
Revenue	1,570	433	2,075	810
Shipment-based | International
Disaggregation of Revenue [Line Items]
Revenue	$ 8,904	$ 10,716	$ 16,271	$ 17,661