Note 7 - Stockholders' Equity (Details Textual)			3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 14, 2022 USD ($) $ / shares shares	Feb. 14, 2018	Jun. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2021 USD ($) shares	Dec. 31, 2021 $ / shares shares	Mar. 31, 2022 shares	Feb. 16, 2018 $ / shares
Preferred Stock, Shares Authorized (in shares)			5,000,000		5,000,000		5,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares			$ 0.001		$ 0.001		$ 0.001
Preferred Stock, Shares Issued (in shares)			56,451		56,451		56,451
Preferred Stock, Shares Outstanding, Ending Balance (in shares)			56,451		56,451		56,451
Stock Issued During Period, Shares, New Issues (in shares)					326,466
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)			1,006,285		1,006,285		132,265
Preferred Stock Redemption Discount | $					$ 5,111,000
Common Stock, Shares Authorized (in shares)			100,000,000		100,000,000		100,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares			$ 0.001		$ 0.001		$ 0.001
Common Stock, Shares, Issued (in shares)			6,081,333		6,081,333		4,778,263
Common Stock, Shares, Outstanding, Ending Balance (in shares)			6,081,333		6,081,333		4,778,263
Share Price (in dollars per share) | $ / shares			$ 1.46		$ 1.46
Share-Based Payment Arrangement, Expense | $			$ 36,000	$ 303,000	$ 88,000	$ 721,000
Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $			100,000		$ 100,000
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)					3 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Fair Value | $			100,000		$ 100,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | $					3,000	88,000
Share-Based Payment Arrangement, Expense | $			$ 36,000	300,000	$ 100,000	700,000
Restricted Stock Units (RSUs) [Member] | Minimum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)					3 years
The 2015 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)			9,482		9,482
Officer and Director Share Purchase Plan [Member]
Common Stock, Shares, Issued (in shares)								0
Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input	5.5
Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input	136.61
Measurement Input, Discount Rate [Member]
Warrants and Rights Outstanding, Measurement Input	1.51
Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input	0
Common Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	807,500
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	$ 9.60
Warrants and Rights Outstanding, Term (Year)	5 years
Common Stock Warrants, Issued with Series D Convertible Preferred Stock [Member]
Proceeds from Issuance of Warrants | $	$ 3,591
Placement agent warrants issued in the January 2022 financing [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	66,500		66,500		66,500
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	$ 10.00		$ 10.00		$ 10.00
Warrants and Rights Outstanding, Term (Year)	5 years
January 2022 Public Offering [Member]
Proceeds from Issuance of Convertible Preferred Stock | $	$ 4,009
Conversion of Series B Preferred Stock into Common Stock [Member]
Conversion of Stock, Shares Converted (in shares)							93
Conversion of Stock, Shares Issued (in shares)							18,600
Series A Preferred Stock [Member]
Preferred Stock, Shares Outstanding, Ending Balance (in shares)			56,366		56,366
Preferred Stock, Liquidation Preference Per Share (in dollars per share) | $ / shares			$ 1,000		$ 1,000
Preferred Stock, Convertible, Conversion Price (in dollars per share) | $ / shares			$ 400		$ 400
Dividends, Preferred Stock, Total | $			$ 1,100,000	$ 1,000,000.0	$ 2,300,000	$ 2,100,000
Series A Preferred Stock [Member] | CRG [Member]
Preferred Stock Dividends, Shares (in shares)							4,175
Series A Preferred Stock [Member] | Conversion of Principal Amount of Senior Secured Loan to Newly Authorized Series A Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage		8.00%
Series B Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares									$ 0.001
Preferred Stock, Shares Outstanding, Ending Balance (in shares)			85		85		85
Preferred Stock, Convertible, Conversion Price (in dollars per share) | $ / shares			$ 5		$ 5		$ 5
Series D Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares	$ 0.001
Conversion of Stock, Shares Converted (in shares)			2,400		7,600
Conversion of Stock, Shares Issued (in shares)			300,000			950,000
Series D Preferred Stock [Member] | Common Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	$ 9.60
Warrants and Rights Outstanding, Term (Year)	5 years
Series D Preferred Stock [Member] | Placement agent warrants issued in the January 2022 financing [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	66,500
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	$ 10.00
Warrants and Rights Outstanding, Term (Year)	5 years
Series D Preferred Stock [Member] | January 2022 offering [Member]
Preferred Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares	$ 0.001
Preferred Stock, Convertible, Conversion Price (in dollars per share) | $ / shares	$ 8.00
Stock Issued During Period, Shares, New Issues (in shares)	7,600
Shares Issued, Price Per Share (in dollars per share) | $ / shares	$ 1,000
Preferred Stock, Convertible, Shares Issuable (in shares)	950,000
Series D Preferred Stock [Member] | January 2022 offering [Member] | Common Warrants [Member]
Conversion of Warrants Allowed Maximum Ownership of Common Stock Percentage	4.99%
Conversion of Warrants Allowed Maximum Ownership of Common Stock Percentage upon Election	9.99%
Series D Preferred Stock [Member] | January 2022 Public Offering [Member]
Preferred Stock, Convertible, Conversion Price (in dollars per share) | $ / shares	$ 8.00
Stock Issued During Period, Shares, New Issues (in shares)	7,600
Shares Issued, Price Per Share (in dollars per share) | $ / shares	$ 1,000