Note 10 - Share-based Compensation - Stock Option Activity (Details) - $ / shares		9 Months Ended	12 Months Ended
	Jan. 29, 2020	Sep. 30, 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 219 days	6 years 219 days
Stock options granted (in shares)	515,036	300,432
Stock options granted, weighted average exercise price (in dollars per share)	$ 5.32	$ 3.15
Stock options exercised (in shares)
Stock options exercised, weighted average exercise price (in dollars per share)
Stock options canceled (in shares)		(43,083)
Stock options canceled, weighted average exercise price (in dollars per share)		$ 13.19
Stock options outstanding, end of period (in shares)		1,078,813	821,464
Balance, weighted average exercise price, end of period (in dollars per share)		$ 6.04	$ 18.99
Exercisable and vested (in shares)		574,574
Exercisable and vested, weighted average exercise price (in dollars per share)		$ 7.77
Exercisable and vested, weighted average remaining contractual term (Year)		6 years 146 days