Note 10 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares shares in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Potentially dilutive common shares (in shares)		31,363	26,876	31,226	25,983
Unvested Stock [Member]
Potentially dilutive common shares (in shares)	[1]	930	605	1,034	548
Convertible Preferred Stocks [Member]
Potentially dilutive common shares (in shares)		16,380	12,647	16,143	11,891
Common Stock Warrants [Member]
Potentially dilutive common shares (in shares)		1,971	1,542	1,967	1,462
IPO Warrants [Member]
Potentially dilutive common shares (in shares)	[2]	12,082	12,082	12,082	12,082

[1] Does not include 3.0 million shares for each of the three and six months ended June 30, 2020 and 4.1 million shares for the three and six months ended June 30, 2019, of unvested stock because the performance conditions had not yet been satisfied as of June 30, 2020 and 2019, 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.