Note 11 - Share-based Compensation - Stock Option Activity (Details) - USD ($)		12 Months Ended
	Jan. 29, 2020	Dec. 31, 2020	Dec. 31, 2019
Stock options outstanding, beginning of period (in shares)		821,464
Balance, weighted average exercise price, beginning of period (in dollars per share)		$ 18.99
Stock options outstanding, weighted average remaining contractual term (Year)		7 years 182 days	7 years 219 days
Stock options outstanding, aggregate intrinsic value		$ 177,100
Stock options granted (in shares)	515,036	342,232
Stock options granted, weighted average exercise price (in dollars per share)	$ 5.32	$ 3.10
Stock options exercised (in shares)
Stock options exercised, weighted average exercise price (in dollars per share)
Stock options cancelled (in shares)		(49,390)
Stock options canceled, weighted average exercise price (in dollars per share)		$ 12.79
Stock options outstanding, end of period (in shares)		1,114,306	821,464
Balance, weighted average exercise price, end of period (in dollars per share)		$ 5.89	$ 18.99
Options exercisable (in shares)		615,470
Options exercisable, weighted average exercise price (in dollars per share)		$ 7.51
Options exercisable, weighted average remaining contractual term (Year)		6 years 109 days
Options exercisable, aggregate intrinsic value		$ 15,600
Options vested and expected to vest (in shares)		1,114,306
Options vested and expected to vest, weighted average exercise price (in dollars per share)		$ 5.89
Options vested and expected to vest, weighted average remaining contractual term (Year)		7 years 182 days
Options vested and expected to vest, aggregate intrinsic value		$ 177,100