Note 9 - Stock Options and Stock-based Employee Compensation - Summary of Stock Option Activity (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Shares Outstanding, Beginning Balance (in shares) | shares	1,903
Weighted Average Exercise Price, Outstanding, at Beginning Period (in dollars per share) | $ / shares	$ 15.57
Shares Granted (in shares) | shares	1,339
Weighted Average Exercise Price, Granted (in dollars per share) | $ / shares	$ 5.46
Shares Forfeited or Expired (in shares) | shares	(2)
Weighted Average Exercise Price, Forfeited or Expired (in dollars per share) | $ / shares	$ 11.85
Shares Outstanding, Ending Balance (in shares) | shares	3,240
Weighted Average Exercise Price, Outstanding, at Ending Period (in dollars per share) | $ / shares	$ 11.39
Weighted Average Remaining Contractual Life, Outstanding (Year)	8 years 219 days
Shares Vested and Exercisable (in shares) | shares	1,353
Weighted Average Exercise Price, Vested and Exercisable (in dollars per share) | $ / shares	$ 17.19
Weighted Average Remaining Contractual Life, Vested and Exercisable (Year)	7 years 182 days
Vested and expected to vest (in shares) | shares	3,020
Weighted Average Exercise Price, Vested and Expected to Vest (in dollars per share) | $ / shares	$ 11.50
Weighted Average Remaining Contractual Life, Vested and Expected to Vest (Year)	8 years 182 days