Note 8 - Stock-based Compensation - Changes in the Number and Weighted-Average Grant-Date Fair Value (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Non-vested stock option awards (in shares) | shares	11,688
Weighted average grant-date fair value (in dollars per share) | $ / shares	$ 3.77
Stock option awards granted (in shares) | shares	10,471
Stock option awards granted (in dollars per share) | $ / shares	$ 4.69
Stock option awards vested (in shares) | shares	(4,543)
Stock option awards vested (in dollars per share) | $ / shares	$ 4.12
Stock option awards forfeited (in shares) | shares	(1,596)
Stock option awards forfeited (in dollars per share) | $ / shares	$ 3.96
Non-vested stock option awards (in shares) | shares	16,020
Weighted average grant-date fair value (in dollars per share) | $ / shares	$ 4.25