Note 12 - Equity Offerings (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			6 Months Ended
	Jan. 29, 2021	Jan. 12, 2021	Jun. 30, 2022	Jun. 30, 2021	Mar. 18, 2022	May 19, 2021	Oct. 09, 2020
Stock Issued During Period, Shares, New Issues (in shares)			19,451,848
Shares Issued, Price Per Share (in dollars per share)			$ 1.50
Proceeds from Issuance of Common Stock, Net			$ 0	$ 130,314
Proceeds from Warrant Exercises				$ 30,600
The 2020 ATM Offering [Member]
Stock Offering Agreement, Maximum Share Value							$ 40,000
Stock Issued During Period, Shares, New Issues (in shares)			19,120,037
Shares Issued, Price Per Share (in dollars per share)			$ 1.47
Public Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)	26,545,832
Shares Issued, Price Per Share (in dollars per share)	$ 3.00
Proceeds from Issuance of Common Stock, Net	$ 73,400
Registered Direct Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)		25,000,000
Shares Issued, Price Per Share (in dollars per share)		$ 1.25
Proceeds from Issuance of Common Stock, Net		$ 28,600
The 2021 ATM Offering [Member]
Stock Offering Agreement, Maximum Share Value						$ 100,000
Stock Issued During Period, Shares, New Issues (in shares)			331,811
Shares Issued, Price Per Share (in dollars per share)			$ 3.47
The 2022 ATM Offering [Member]
Stock Offering Agreement, Maximum Share Value					$ 100,000
Stock Issued During Period, Shares, New Issues (in shares)			0