Description of Business and Summary of Significant Accounting Policies (Textual) (Details) $ / shares in Units, shares in Thousands	1 Months Ended		12 Months Ended
	Aug. 31, 2018 USD ($) $ / shares shares	May 31, 2018 USD ($)	Dec. 31, 2018 USD ($) manufacturing_location contract_manufacturer	Dec. 31, 2017 USD ($)	Dec. 19, 2018 USD ($)	Dec. 31, 2016 USD ($)
Description of Business and Summary of Significant Accounting Policies [Line Items]
Manufacturing locations | manufacturing_location			2
Stock issued in public offering, shares | shares	7,590
Price per share | $ / shares	$ 3.25
Proceeds from sale of common stock, net of offering costs	$ 23,000,000		$ 22,950,000	$ 0
Cash and cash equivalents			58,028,000	46,192,000
Working capital			86,100,000
Interest income reclassified			(4,460,000)	(1,413,000)
Leasehold improvements funded by landlords			1,000,000	1,200,000
Deferred rent related to leasehold improvements funding by landlords			1,000,000	1,200,000
Equipment purchased under capital leases			1,911,000	0
Goodwill impairment			0	0
Impairment of assets			$ 218,000	240,000
Standard product warranty, term, minimum			1 year
Standard product warranty, term, maximum			8 years
Accrued warranty			$ 944,000	1,315,000		$ 910,000
FDIC insurance limit			250,000
Research and development expense			19,983,000	16,342,000
Third party funding offset			200,000	2,500,000
Advertising expense			300,000	400,000
Cost of revenue			80,459,000	82,407,000
Selling, general and administrative			$ 30,542,000	38,186,000
Joint Development Agreement for Technologies for Automotive Market
Description of Business and Summary of Significant Accounting Policies [Line Items]
Cash consideration under joint development agreement				2,200,000
Minimum
Description of Business and Summary of Significant Accounting Policies [Line Items]
Estimated useful lives of property and equipment (in years)			3 years
Estimated useful life (in years)			8 years
Maximum
Description of Business and Summary of Significant Accounting Policies [Line Items]
Estimated useful lives of property and equipment (in years)			10 years
Estimated useful life (in years)			14 years
China
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of contract manufacturers | contract_manufacturer			2
Discontinued Operations, Disposed of by Sale
Description of Business and Summary of Significant Accounting Policies [Line Items]
Percentage of shares sold					100.00%
Purchase price					$ 55,055,000
Net cash proceeds received					$ 47,814,000
Scenario, Adjustment | Accounting Standards Update 2017-07
Description of Business and Summary of Significant Accounting Policies [Line Items]
Interest income reclassified				79,000
Research and development expense				8,000
Cost of revenue				39,000
Selling, general and administrative				$ 8,000
Line of Credit
Description of Business and Summary of Significant Accounting Policies [Line Items]
Borrowings outstanding			$ 0
I2BF
Description of Business and Summary of Significant Accounting Policies [Line Items]
Payments received by related party		$ 282,000
Titan
Description of Business and Summary of Significant Accounting Policies [Line Items]
Revenues			$ 397,000