Revenue Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total Revenue	$ 34,693	$ 34,756	$ 44,740	$ 42,284	$ 44,003	$ 45,986	$ 48,556	$ 42,612	$ 156,473	$ 181,157	$ 192,925
United States
Disaggregation of Revenue [Line Items]
Total Revenue									109,093	123,209	136,111
International
Disaggregation of Revenue [Line Items]
Total Revenue									47,380	57,948	56,814
Implant-based
Disaggregation of Revenue [Line Items]
Total Revenue									127,111	143,818	160,618
Implant-based | United States
Disaggregation of Revenue [Line Items]
Total Revenue									106,014	120,572	133,734
Implant-based | International
Disaggregation of Revenue [Line Items]
Total Revenue									21,097	23,246	26,884
Shipment-based
Disaggregation of Revenue [Line Items]
Total Revenue									29,362	37,339	32,307
Shipment-based | United States
Disaggregation of Revenue [Line Items]
Total Revenue									3,079	2,637	2,377
Shipment-based | International
Disaggregation of Revenue [Line Items]
Total Revenue									$ 26,283	$ 34,702	$ 29,930