Balance Sheet Details - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Gross	$ 32,835	$ 32,362
Less accumulated amortization	(27,587)	(26,651)
Intangible assets, net	5,248	5,711
Amortization of intangible assets	900	1,600
Impairment of intangible assets		1,736
Developed product technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Gross	13,876	13,876
Intellectual property
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Gross	$ 1,004	1,004
License agreements
Finite-Lived Intangible Assets [Line Items]
Useful lives	2 years
Intangible assets, Gross	$ 5,738	5,265
License agreements | Epicage Interbody Fusion Device
Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets		500
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Gross	$ 732	732
Customer-related
Finite-Lived Intangible Assets [Line Items]
Useful lives	8 years
Intangible assets, Gross	$ 7,458	7,458
Distribution network
Finite-Lived Intangible Assets [Line Items]
Useful lives	8 years
Intangible assets, Gross	$ 4,027	$ 4,027