Note 13 - Equity Incentive Plans - Summary of Stock Option Transactions (Details) - $ / shares		12 Months Ended
	Mar. 24, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares available for grant, balance (in shares)		295,180	200,650
Number of options outstanding, beginning balance (in shares)		1,811,652	865,163	304,850
Weighted average exercise price, balance (in dollars per share)		$ 2.74	$ 8.13	$ 9.50
Shares available for grant, assumed on consummation of Merger (in shares)				291,102
Number of options outstanding, assumed on consummation of Merger (in shares)				627,106
Weighted average exercise price, assumed on consummation of Merger (in dollars per share)				$ 26.33
Shares available for grant, granted (in shares)		(5,579,800)	(1,791,030)	(431,100)
Number of options outstanding, granted (in shares)	2,610,000	5,579,800	1,791,030	431,100
Weighted average exercise price, granted (in dollars per share)	$ 1.70	$ 2.66	$ 0.67	$ 5.17
Number of options outstanding, exercised (in shares)		(414,676)	0	(2,013)
Weighted average exercise price, exercised (in dollars per share)		$ 1.45		$ 6.49
Shares available for grant, forfeited (in shares)		105,910	483,849	71,500
Number of options outstanding, forfeited (in shares)		(105,992)	(592,528)	(89,903)
Weighted average exercise price, forfeited (in dollars per share)		$ 1.65	$ 1.57	$ 5.90
Shares available for grant, canceled (in shares)		9,573	25,100	269,148
Number of options outstanding, canceled (in shares)		(57,751)	(252,013)	(405,977)
Weighted average exercise price, canceled (in dollars per share)		$ 10.57	$ 9.25	$ 34.64
Shares availabe for grant, 2019 Plan Amendment (in shares)		6,400,000	1,600,000
Shares available for grant, removed from 2016 Plan (in shares)			(223,389)
Shares available for grant, balance (in shares)		1,230,863	295,180	200,650
Number of options outstanding, balance (in shares)		6,813,033	1,811,652	865,163
Weighted average exercise price, balance (in dollars per share)		$ 2.70	$ 2.74	$ 8.13