Note 11 - Net Loss Per Share Attributable to Common Stockholders - Anti-dilutive Securities (Details) - shares shares in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Potentially dilutive common shares (in shares)		31,609	28,302
Unvested Stock [Member]
Potentially dilutive common shares (in shares)	[1]	916	861
Convertible Preferred Stocks [Member]
Potentially dilutive common shares (in shares)		16,635	13,697
Common Stock Warrants [Member]
Potentially dilutive common shares (in shares)		1,976	1,662
IPO Warrants [Member]
Potentially dilutive common shares (in shares)	[2]	12,082	12,082

[1] Does not include 2.1 million shares and 3.6 million shares of unvested stock for the year ended December 31, 2020 and 2019 because the performance conditions had not yet been satisfied as of December 31, 2020 and 2019, respectively.

[2] The IPO Warrants were issued in connection with our initial public offering and are exercisable at a price of $11.50 per share and expire July 24, 2022. The Company may redeem the Warrants at a price of $0.01 per IPO Warrant upon 30 days’ notice only if the last sale price of our common stock is at least $17.50 per share for any 20 trading days within a 30-trading day period. If the Company redeems the IPO Warrants in this manner, the Company will have the option to do so on a cashless basis with the issuance of an economically equivalent number of shares of Company common stock.