Note 1 - The Company and Basis of Presentation (Details Textual) - USD ($)						1 Months Ended		3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 22, 2021	Dec. 11, 2020	Jul. 21, 2020	Jun. 22, 2020	Sep. 30, 2021	Jul. 21, 2020	Oct. 03, 2021	Sep. 27, 2020	Jun. 28, 2020	Oct. 03, 2021	Sep. 27, 2020	Aug. 16, 2021	Jan. 03, 2021	May 06, 2020
Restructuring Charges, Total											$ 0	$ 624,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance								$ 19,581,000			19,581,000			$ 22,748,000
Line of Credit, Current								15,000,000			15,000,000			15,000,000
Notes Payable, Noncurrent, Total								$ 0			$ 0			$ 1,192,000
Common Stock, Par or Stated Value Per Share (in dollars per share)								$ 0.001			$ 0.001			$ 0.001
Proceeds from Issuance of Common Stock											$ 148,000	$ 0
Underwritten Public Offering [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)								199,000	142,000	2,500,000
Common Stock [Member] | Underwritten Public Offering [Member]
Proceeds from Issuance of Common Stock, Net							$ 8,100,000
Stock Issued During Period, Shares, New Issues (in shares)					2,500,000
Shares Issued, Price Per Share (in dollars per share)					$ 3.50
Proceeds from Issuance of Common Stock					$ 8,800,000		9,300,000
Payments of Stock Issuance Costs					$ 1,100,000		$ 1,200,000
Common Stock [Member] | Exercise of Option for Overallotment of Shares by Underwriters [Member]
Stock Issued During Period, Shares, New Issues (in shares)				141,733	375,000
Proceeds from Issuance of Common Stock				$ 496,000
Payments of Stock Issuance Costs				$ 52,000
Common Stock [Member] | Share Subscription Agreement [Member]
Proceeds from Issuance of Common Stock, Net	$ 1,000,000.0
Stock Issued During Period, Shares, New Issues (in shares)	73,664	125,000
Payments of Stock Issuance Costs	$ 45,000
Heritage Bank of Commerce [Member] | Paycheck Protection Program [Member]
Notes Payable, Noncurrent, Total								$ 1,200,000			1,200,000
Proceeds from Issuance of Common Stock, Net						$ 1,000,000.0
Debt Instrument, Face Amount															$ 1,200,000
Heritage Bank of Commerce [Member] | Revolving Credit Facility [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance								19,600,000			19,600,000
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
Minimum Cash Required for Covenant Related to Credit Facility													$ 3,000,000.0
Debt Instrument, Interest Rate, Effective Percentage								3.75%			3.75%			3.75%
Heritage Bank of Commerce [Member] | Revolving Credit Facility [Member] | Prime Rate [Member]
Debt Instrument, Basis Spread on Variable Rate			0.50%