Note 9 - Stock-based Employee Compensation - Summary of Stock Option Activity (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2022 $ / shares shares
Shares Outstanding, Beginning Balance (in shares) | shares	3,387
Weighted Average Exercise Price, Outstanding, at Beginning Period (in dollars per share) | $ / shares	$ 9.74
Shares Granted (in shares) | shares	835
Weighted Average Exercise Price, Granted (in dollars per share) | $ / shares	$ 1.02
Shares Forfeited or Expired (in shares) | shares	(49)
Weighted Average Exercise Price, Forfeited or Expired (in dollars per share) | $ / shares	$ 6.06
Shares Outstanding, Ending Balance (in shares) | shares	4,173
Weighted Average Exercise Price, Outstanding, at Ending Period (in dollars per share) | $ / shares	$ 8.04
Weighted Average Remaining Contractual Life, Outstanding (Year)	8 years 2 months 12 days
Shares Vested and Exercisable (in shares) | shares	2,142
Weighted Average Exercise Price, Vested and Exercisable (in dollars per share) | $ / shares	$ 12.38
Weighted Average Remaining Contractual Life, Vested and Exercisable (Year)	7 years 1 month 6 days
Vested and expected to vest (in shares) | shares	3,925
Weighted Average Exercise Price, Vested and Expected to Vest (in dollars per share) | $ / shares	$ 8.06
Weighted Average Remaining Contractual Life, Vested and Expected to Vest (Year)	8 years 2 months 12 days