Note 12 - Stockholders' Equity - Unvested Restricted Stock (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Unvested, shares (in shares)	2,022,352
Restricted Stock Units (RSUs) [Member]
Unvested, shares (in shares)	3,936,134	3,997,168	2,689,468
Unvested, weighted average fair value per share (in dollars per share)	$ 2.55	$ 2.46	$ 4.14
Granted, shares (in shares)	629,437	1,688,111	3,312,481
Granted (unvested), weighted average fair value per share (in dollars per share)	$ 7.88	$ 3.03	$ 1.85
Canceled, shares (in shares)	(770,416)	(70,236)	(803,683)
Canceled, weighted average fair value per share (in dollars per share)	$ 2.82	$ 2.08	$ 2.62
Distributed, shares (in shares)	(1,772,803)	(1,678,909)	(1,201,098)
Distributed (vested), weighted average fair value per share (in dollars per share)	$ 2.60	$ 2.83	$ 4.00
Unvested, shares (in shares)	2,022,352	3,936,134	3,997,168
Unvested, weighted average fair value per share (in dollars per share)	$ 3.97	$ 2.55	$ 2.46