Description of Business and Basis of Presentation (Details Textual) $ / shares in Units, shares in Thousands	1 Months Ended		3 Months Ended
	Aug. 31, 2018 USD ($) $ / shares shares	Oct. 11, 2017 USD ($)	Mar. 31, 2019 USD ($) manufacturing_location contract_manufacturer	Mar. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 19, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 16, 2017 USD ($)	Sep. 25, 2017 USD ($)
Description of Business and Basis of Presentation [Line Items]
Manufacturing locations | manufacturing_location			2
Description of Business and Basis of Presentation (Textual) [Abstract]
Warranty period, minimum, in years			1 year
Warranty period, maximum, in years			8 years
Accrued warranty liability			$ 998,000	$ 1,157,000		$ 944,000		$ 1,315,000
Cash and cash equivalents			48,128,000			58,028,000
Working capital amount			72,400,000
Cost of revenue			16,966,000	19,684,000
Selling, general and administrative			9,700,000	7,783,000
Research and development			5,165,000	4,908,000
Offering shares of common stock | shares	7,590
Offering price per share | $ / shares	$ 3.25
Proceeds from sale of common stock, net of offering costs	$ 23,000,000
Use of cash from operations			(9,033,000)	(11,211,000)
Value of securities permitted for issuance under shelf registration									$ 125,000,000
Operating lease right-of-use assets			8,683,000			0
Lease liability			11,076,000
Accounting Standards Update 2016-02
Description of Business and Basis of Presentation (Textual) [Abstract]
Operating lease right-of-use assets					$ 9,100,000
Lease liability					$ 11,600,000
Line of Credit
Description of Business and Basis of Presentation (Textual) [Abstract]
Borrowings outstanding			0
Revolving Credit Facility | East West Bank
Description of Business and Basis of Presentation (Textual) [Abstract]
Amount available under revolving line of credit			$ 5,800,000
Minimum
Description of Business and Basis of Presentation (Textual) [Abstract]
Estimated useful life (in years)			8 years
Maximum
Description of Business and Basis of Presentation (Textual) [Abstract]
Estimated useful life (in years)			14 years
China
Description of Business and Basis of Presentation [Line Items]
Number of contract manufacturers | contract_manufacturer			2
Convertible Senior Notes due 2022
Description of Business and Basis of Presentation (Textual) [Abstract]
Proceeds received		$ 43,000,000
Principal amount		$ 6,000,000	$ 46,000,000			$ 46,000,000				$ 40,000,000
Scenario, Adjustment
Description of Business and Basis of Presentation [Line Items]
Interest income reclassified				$ 71,000
Discontinued Operations, Disposed of by Sale
Description of Business and Basis of Presentation [Line Items]
Percentage of shares sold							100.00%
Description of Business and Basis of Presentation (Textual) [Abstract]
Purchase price							$ 55,055,000
Net cash proceeds received							$ 47,814,000
Titan Power Solution LLS
Description of Business and Basis of Presentation [Line Items]
Revenue from related parties			59,000
Accounts receivable related to related parties			$ 59,000