Note 8 - Stock-based Compensation Expense - Restricted Stock Units (Details) - Restricted Stock Units (RSUs) [Member]	3 Months Ended
	Mar. 31, 2022 $ / shares shares
Non-vested shares, beginning of year (in shares) | shares	3,018,788
Non-vested shares, beginning of year, weighted average grant date fair value (in dollars per share) | $ / shares	$ 4.58
Granted (in shares) | shares	2,810,414
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	$ 1.94
Vested (in shares) | shares	(1,332,788)
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	$ 1.96
Forfeited (in shares) | shares	(2,000,000)
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares	$ 5.46
Non-vested shares, end of period (in shares) | shares	2,496,414
Non-vested shares, end of period, weighted average grant date fair value (in dollars per share) | $ / shares	$ 2.30