Note 9 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares shares in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Potentially dilutive common shares (in shares)		43,639	31,363	42,389	31,226
Unvested Stock [Member]
Potentially dilutive common shares (in shares)	[1]	1,555	930	1,453	1,034
Convertible Preferred Stocks [Member]
Potentially dilutive common shares (in shares)		27,129	16,380	26,380	16,143
Common Stock Warrants [Member]
Potentially dilutive common shares (in shares)		2,873	1,971	2,474	1,967
IPO Warrants [Member]
Potentially dilutive common shares (in shares)	[2]	12,082	12,082	12,082	12,082

[1] Does not include 2.6 million shares for each of the three and six months ended June 30, 2021 and 3.0 million shares for each of the three and six months ended June 30, 2020, of unvested stock because the performance conditions had not yet been satisfied as of June 30, 2021 and 2020, respectively.

[2] The IPO Warrants were issued in connection with our initial public offering in 2015. The IPO Warrants are exercisable at a price of $11.50 per share and expire on July 24, 2022. The Company may redeem the IPO 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.