Note 9 - Stockholders' Equity (Details Textual) - USD ($)								12 Months Ended
	Mar. 29, 2021	Dec. 18, 2020	Dec. 16, 2020	Jun. 19, 2020	Jun. 17, 2020	Jun. 08, 2020	Sep. 04, 2019	Dec. 31, 2021	Dec. 31, 2020	Aug. 06, 2019
Common Stock, Par or Stated Value Per Share (in dollars per share)								$ 0.001	$ 0.001
Stock Issued During Period, Value, New Issues								$ 1,942,000
Proceeds from Issuance of Common Stock								2,001,000	$ 0
Stock Issued During Period, Value, Issued for Services									148,000
Two Former Board Members [Member]
Stock Issued During Period, Shares, Issued for Services (in shares)						29,625
Stock Issued During Period, Value, Issued for Services						$ 148,000
Underwriters [Member]
Stock Issued During Period, Shares, New Issues (in shares)							75,000
The $10.5 Million Registered Direct Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)		2,038,836
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.001
Shares Issued, Price Per Share (in dollars per share)		$ 5.15
Stock Issued During Period, Value, New Issues		$ 10,500,000							9,765,000
Placement Agent Fee		7.00%
Proceeds from Issuance of Common Stock		$ 9,800,000						0	10,500,000
The $8.5 Million Registered Direct Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)			1,789,474
Common Stock, Par or Stated Value Per Share (in dollars per share)			$ 0.001
Shares Issued, Price Per Share (in dollars per share)			$ 4.75
Stock Issued During Period, Value, New Issues			$ 8,500,000						7,827,000
Placement Agent Fee			7.00%
Proceeds from Issuance of Common Stock			$ 7,800,000					0	8,500,000
Placement Agent Maximum Expenses Reimbursement Amount			$ 40,000
Public Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)				4,762,000
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001
Shares Issued, Price Per Share (in dollars per share)				$ 2.10
Stock Issued During Period, Value, New Issues									10,273,000
Proceeds from Issuance of Common Stock				$ 10,300,000				$ 0	$ 11,500,000
Underwriters, Additional Common Shares Authorized to Purchase (in shares)					714,190
Purchase Agreement with Lincoln Park [Member]
Stock Issued During Period, Shares, New Issues (in shares)	373,832							0
Shares Issued, Price Per Share (in dollars per share)	$ 5.35
Proceeds from Issuance of Common Stock	$ 2,000,000
Sale of Stock, Aggregate Value, Maximum	$ 20,000,000
Stock Issuable, Commitment Shares on Pro Rata Basis (in shares)	50,000
Stock Issued During the Period, Shares, Commission Fees (in shares)	80,000
Stock Issued During the Period, Commitment Shares Issued on Pro Rata Basis (in shares)	5,000
Conditional Issuance, Maximum Number of Shares Allowed to be Purchased (in shares)	100,000
Stock Purchase Agreement Accelerated Purchase, Maximum, Percent of Shares Purchased on the Same Trading Day	300.00%
Stock Purchase Agreement Accelerated Purchase, Maximum, Percent of Total Common Shares Traded During Specified Period	30.00%
Maximum Number of Shares Allowed to be Issued Including Commitment Shares (in shares)	3,266,177
Percentage of Common Stock Outstanding	19.99%
Private Placement Unit [Member]
Number of Common Stock in Each Unit (in shares)										1