Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands					3 Months Ended					12 Months Ended
		Dec. 08, 2019	Sep. 30, 2019	Jan. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Income (Loss) Attributable to Parent, Total										$ (1,129)	$ (17,325)	$ (12,589)
Net Cash Provided by (Used in) Operating Activities, Total										(11,518)	(12,283)	(9,369)
Retained Earnings (Accumulated Deficit), Ending Balance					$ (122,234)	$ (123,993)				(122,234)	(123,993)
Working Capital					25,700					25,700
Proceeds from Divestiture of Businesses										35,396
Gain (Loss) on Disposition of Business										14,100
Cash, FDIC Insured Amount					1,000	300				1,000	300
Cash and Cash Equivalents in Foreign Accounts					300	67				300	67
Restricted Cash, Noncurrent					0	523				0	523
Notes Receivable, Fair Value Disclosure					5,000					5,000
Financing Receivable, after Allowance for Credit Loss, Noncurrent, Total					3,253					3,253
Proceeds from Collection of Notes Receivable										313	19	39
Investment in Convertible Note Receivable, Noncurrent						655					655
Accounts Receivable, Allowance for Credit Loss, Current					47	17				47	17
Reclassified Deposits and Other Assets to Prepaid Assets						100					100
Asset Impairment Charges, Other than Goodwill										0	0	0
Goodwill, Ending Balance					0	0		$ 4,549		0	0	4,549
Goodwill, Impairment Loss						3,100	$ 1,300	$ 3,200			4,347	3,152
Accrued Liabilities, Current, Total					5,159	1,893				5,159	1,893
Employee-related Liabilities, Current, Total					1,100	900				1,100	900
Accounts Payable, Trade, Current					200	$ 100				200	100
Accrued Expenses, Working Capital Adjustment					$ 2,800					2,800
Derivative, Gain on Derivative											129	111
Payments for Derivative Instrument, Financing Activities											227
Advertising Expense										$ 400	600	500
Number of Operating Segments										3
Number of Reportable Segments										2
Depreciation and Amortization, Discontinued Operations										$ 800	$ 1,500	$ 1,500
Royalty Agreement [Member]
Weighted Average Shares Outstanding, Unissued					37,312	1,844		63,602		37,312	1,844	63,602
Transferred at Point in Time [Member]
Percentage of Revenue From Goods and Services										29.00%	22.00%
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				$ 1,900
CUI Global Inc. [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match										6.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount										$ 200	$ 100	$ 74
Developed Technology Rights [Member]
Finite-Lived Intangible Asset, Useful Life	[1]									20 years
Deposits and Other Assets [Member]
Asset Impairment Charges, Total						$ 1,500
Test Products International Inc. [Member]
Note Receivable Interest Rate									5.00%
Notes Receivable, Related Parties									$ 400
Investment Income, Interest										$ 8	17	18
Royalty Expense										36	10	16
Royalty Expense, Offset Against Note Receivable										13	10	16
Proceeds from Collection of Notes Receivable											19	39
Financing Receivable, after Allowance for Credit Loss, Total					$ 0	318				0	318
VPS [Member]
Investment in Convertible Note Receivable, Noncurrent						655					655
JAPAN
Cash, Uninsured Amount					200	300				200	300
Europe [Member]
Cash, Uninsured Amount					600	0				600	0
CANADA
Cash, Uninsured Amount					200	67				200	67
Bel Fuse Inc [Member]
Asset Sale Agreement, Sale Price		$ 32,000
Power and Electromechanical Business [Member] | Discontinued Operations, Disposed of by Sale [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount										300	400	300
Power and Electromechanical Segment [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				900
Power and Electromechanical Segment [Member] | CUI Canada [Member]
Finite-Lived Customer Relationships, Gross					92					92
Goodwill, Ending Balance					0					0
Power and Electromechanical Segment [Member] | CUI Japan [Member]
Goodwill, Ending Balance					0					0
Power and Electromechanical Segment [Member] | Power and Electromechanical Business [Member] | Discontinued Operations, Disposed of by Sale [Member]
Proceeds from Divestiture of Businesses					35,400
Gain (Loss) on Disposition of Business					$ 14,100
Power and Electromechanical Segment [Member] | Power and Electromechanical Business [Member] | Discontinued Operations, Disposed of by Sale [Member] | Electromechanical Subsegment [Member]
Proceeds from Divestiture of Businesses			$ 4,700
Disposal Group, Including Discontinued Operation, Consideration			15,000
Disposal Group, Including Discontinued Operation, Liabilities Assumed			$ 5,300
Disposal Group, Including Discontinued Operation, Earn-out Term			5 years
Disposal Group, Including Discontinued Operation, Consideration, Minimum EBITDA for Earn-out			$ 3,500
Disposal Group, Including Discontinued Operation, Earn-out Consideration			5,000
Disposal Group, Including Discontinued Operation, Earn-out Consideration, Fair Value			$ 3,300
Cash Provided by (Used in) Operating Activities, Discontinued Operations										2,700	4,500	3,700
Cash Provided by (Used in) Investing Activities, Discontinued Operations										$ 500	1,300	1,000
Energy Segment [Member]
Goodwill, Ending Balance								$ 4,549				$ 4,549
Goodwill, Impairment Loss											$ 4,347
Number of Reportable Segments										1
Energy Segment [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				$ 2,800
Energy Segment [Member] | Developed Technology Rights [Member]
Finite-Lived Intangible Asset, Useful Life	[2]									20 years

[1] Technology rights are amortized over a 20-year life or the term of the rights agreement.

[2] All intangibles are reviewed annually for impairment, or sooner if circumstances change.