Note 11 - Stockholders' Equity (Details Textual)						1 Months Ended		12 Months Ended
		Jun. 22, 2020 USD ($) $ / shares shares	Dec. 06, 2019	Jun. 21, 2019 USD ($) $ / shares shares	May 29, 2018 yr $ / shares shares	Jul. 21, 2020 USD ($) shares	May 31, 2018 USD ($) $ / shares shares	Jan. 03, 2021 USD ($) $ / shares shares	Dec. 29, 2019 USD ($) $ / shares shares	Dec. 30, 2018 USD ($) shares	Mar. 15, 2019 USD ($)
Common Stock, Shares Authorized (in shares) | shares								200,000,000	200,000,000
Preferred Stock, Shares Authorized (in shares) | shares								10,000,000	10,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares								$ 0.001	$ 0.001
Proceeds from Issuance of Common Stock								$ 9,296,000	$ 9,437,000	$ 16,215,000
Payments of Stock Issuance Costs								$ 1,147,000	$ 1,181,000	$ 1,638,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares								$ 19.32
Class of Warrant or Right, Outstanding (in shares) | shares								386,100
Warrants Issued in Connection with Underwritten Public Offering [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares) | shares							0.40
Warrants and Rights Outstanding, Term (Month)					60 months
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares					$ 19.32
Class of Warrant or Right, Estimated Grant Date Fair Value (in dollars per share) | $ / shares					$ 7.98
Warrants Issued in Connection with Underwritten Public Offering [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input (Year) | yr					5
Warrants Issued in Connection with Underwritten Public Offering [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input (Year)					0.0258
Warrants Issued in Connection with Underwritten Public Offering [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input (Year)					0.5275
Warrants Issued in Connection with Underwritten Public Offering [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input (Year)					0
Maximum [Member] | Warrants Issued in Connection with Underwritten Public Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | shares							386,100
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares	[1]							2,642,000	1,314,000	965,000
Common Stock [Member] | Maximum [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | shares					386,000
Underwritten Public Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares							965,251
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares		$ 0.001					$ 0.001
Equity Offering Units, Issued, Price Per Unit							16.10
Proceeds from Issuance or Sale of Equity, Total							$ 13,900,000
Underwritten Public Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares		2,500,000		1,300,000
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares		$ 0.001		$ 0.001
Shares Issued, Price Per Share (in dollars per share) | $ / shares		$ 3.50		$ 7.00
Proceeds from Issuance of Common Stock		$ 8,800,000		$ 8,000,000.0		$ 8,100,000
Payments of Stock Issuance Costs		$ 1,100,000
Shelf Registration Maximum Offering											$ 75,000,000
Number Of Common Stocks, Issued, Units (in shares) | shares							1
Exercise of Option for Overallotment of Shares by Underwriters [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares		375,000		171,429		141,733
Proceeds from Issuance of Common Stock						$ 496,000
Payments of Stock Issuance Costs						52,000
Underwritten Public Offering, Including Exercise of Overallotment Options by Underwriters [Member] | Common Stock [Member]
Proceeds from Issuance of Common Stock						9,300,000
Payments of Stock Issuance Costs						1,200,000
Proceeds from Issuance of Common Stock, Net						$ 8,100,000
Reverse Stock Split [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio			14

[1] Common stock, par value and additional paid-in capital amounts are adjusted to reflect 1-for-14 reverse stock split effected on December 23, 2019.