Balance Sheet Details - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 67,045	$ 68,648
Less accumulated depreciation and amortization	(54,375)	(53,572)
Property and equipment, net	12,670	15,076
Depreciation	$ 6,600	7,400
Surgical instruments
Property, Plant and Equipment [Line Items]
Useful lives	4 years
Property and equipment, gross	$ 53,198	53,095
Machinery and equipment
Property, Plant and Equipment [Line Items]
Useful lives	7 years
Property and equipment, gross	$ 5,503	5,435
Capital leased assets, gross	$ 2,100	2,100
Computer equipment
Property, Plant and Equipment [Line Items]
Useful lives	3 years
Property and equipment, gross	$ 3,500	3,511
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Useful lives	5 years
Property and equipment, gross	$ 2,794	2,695
Leasehold improvements
Property, Plant and Equipment [Line Items]
Various useful lives of leasehold improvements	various
Property and equipment, gross	$ 1,714	3,467
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 336	$ 445