Note 12 - Equity Offerings - Summary of Sales Under Offering (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares
Total shares of common stock sold (in shares) | shares	19,472,917
Average price per share (in dollars per share) | $ / shares	$ 1.51
Gross proceeds	$ 29,324
Commission earned by Sales Agents	880
Net proceeds	$ 28,444
The 2021 ATM Offering [Member]
Total shares of common stock sold (in shares) | shares	352,880
Average price per share (in dollars per share) | $ / shares	$ 3.47
Gross proceeds	$ 1,224
Commission earned by Sales Agents	37
Net proceeds	$ 1,187
The 2020 ATM Offering [Member]
Total shares of common stock sold (in shares) | shares	19,120,037
Average price per share (in dollars per share) | $ / shares	$ 1.47
Gross proceeds	$ 28,100
Commission earned by Sales Agents	843
Net proceeds	$ 27,257