Note 11 - Stock-based Compensation - Stock Option Award Activity (Details) - USD ($)		9 Months Ended		12 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Options outstanding (in shares)		1,552
Options outstanding, weighted average exercise price (in dollars per share)	[1]	$ 556.13
Options outstanding, weighted average remaining contractual term (Year)		9 years 10 months 24 days		5 years 7 months 6 days
Granted (in shares)		4,670,324	0
Granted, weighted average exercise price (in dollars per share)	[1]	$ 4.98
Canceled or forfeited (in shares)		(1,597)
Canceled or forfeited, weighted average exercise price (in dollars per share)	[1]	$ 130.67
Exercised (in shares)		0
Exercised, weighted average exercise price (in dollars per share)	[1]	$ 0
Options outstanding (in shares)		4,670,279		1,552
Options outstanding, weighted average exercise price (in dollars per share)	[1]	$ 5.12		$ 556.13
Options outstanding, aggregate intrinsic value		$ 7,750,148
Options exercisable (in shares)		1,515
Options exercisable, weighted average exercise price (in dollars per share)	[1]	$ 431.34
Options exercisable, weighted average remaining contractual term (Year)		4 years 10 months 24 days
Options exercisable, aggregate intrinsic value		$ 0
Options vested and expected to vest (in shares)		4,435,359
Options vested and expected to vest, weighted average exercise price (in dollars per share)	[1]	$ 5.12
Options vested and expected to vest, weighted average remaining contractual term (Year)		9 years 10 months 24 days
Options vested and expected to vest, aggregate intrinsic value		$ 7,360,181

[1] Exercise price of options outstanding range from $4.98 to $56,460 as of September 30, 2021.