Note 1 - The Company and Basis of Presentation (Details Textual)							1 Months Ended	3 Months Ended				9 Months Ended
	Jul. 21, 2020 USD ($) shares	Jun. 22, 2020 USD ($) $ / shares shares	May 06, 2020 USD ($)	Dec. 23, 2019	Nov. 06, 2019	Jun. 21, 2019 USD ($) $ / shares shares	Jul. 21, 2020 USD ($)	Sep. 27, 2020 USD ($) $ / shares shares	Jun. 28, 2020 shares	Jun. 30, 2019 shares	[1]	Sep. 27, 2020 USD ($) $ / shares	Sep. 29, 2019 USD ($)	Dec. 29, 2019 USD ($) $ / shares
Restricted Cash and Cash Equivalents, Current, Total								$ 24,700,000				$ 24,700,000
Line of Credit, Current								$ 15,000,000				15,000,000		$ 15,000,000
Proceeds from Issuance of Debt												$ 1,191,000	$ 0
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares								$ 0.001				$ 0.001		$ 0.001
Proceeds from Issuance of Common Stock												$ 8,099,000	$ 8,258,000
Reverse Stock Split [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio				14								14
Underwritten Public Offering [Member]
Payments of Stock Issuance Costs		$ 1,100,000
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares								142,000	2,500,000	1,314,000
Common Stock [Member] | Underwritten Public Offering [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	$ 9,300,000
Common Stock [Member] | Exercise of Option for Overallotment of Shares by Underwriters [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares	141,733	375,000				171,429
Proceeds from Issuance of Common Stock	$ 500,000
Payments of Stock Issuance Costs	$ 52,000
Common Stock [Member] | Underwritten Public Offering, Including Exercise of Overallotment Options by Underwriters [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
Heritage Bank of Commerce [Member] | Revolving Credit Facility [Member]
Line of Credit, Current								$ 15,000,000.0				$ 15,000,000.0		$ 15,000,000.0
Line of Credit Facility, Expiration Period (Year)					1 year
Debt Instrument, Interest Rate, Stated Percentage					5.50%
Heritage Bank of Commerce [Member] | Revolving Credit Facility [Member] | Prime Rate [Member]
Debt Instrument, Basis Spread on Variable Rate					0.50%
Paycheck Protection Program [Member]
Proceeds from Issuance of Debt			$ 1,200,000									$ 1,200,000

[1] Common stock shares and additional paid-in capital amounts as of December 31, 2018, and in the three-months ended March 31, 2019 and September 29, 2019 are adjusted to reflect 1-for-14 reverse stock split effected on December 23, 2019.