Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounting Policies
Accumulated deficit	$ 168,335,000	$ 152,898,000
Recognized other-than-temporary impairment on marketable securities	0
Materials Inventory
Inventory raw materials noncurrent	3,400,000	4,400,000
Inventory impairment charges	$ 800,000	1,000,000	$ 1,900,000
Impairment of Long-Lived Assets
Impairment loss on intangible assets		0
Impairment expenses		$ 0	$ 0
Revenue Recognition
Number of principal sources from where revenue is derived | item	2
Segment Information
Number of reportable segments | item	1
Fair Value of Financial Instruments
Amount of Level 3 assets	$ 0
Amount of Level 3 liabilities	0
Patents
Impairment of Long-Lived Assets
Impairment loss on intangible assets	$ 1,000,000
Maximum | Patents
Intangible Assets
Intangible assets useful life	20 years
Property and Equipment. | Minimum
Property and Equipment
Estimated useful lives of equipment	3 years
Property and Equipment. | Maximum
Property and Equipment
Estimated useful lives of equipment	5 years
Property And Equipment
Impairment of Long-Lived Assets
Impairment loss	$ 900,000