Note 9 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares shares in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Potentially dilutive common shares (in shares)		29,550	16,342	27,255	13,827
Unvested Stock [Member]
Potentially dilutive common shares (in shares)	[1]	989	513	768	483
Convertible Preferred Stocks [Member]
Potentially dilutive common shares (in shares)		14,678	3,322	12,829	1,119
Common Stock Warrants [Member]
Potentially dilutive common shares (in shares)		1,801	425	1,576	143
IPO Warrants [Member]
Potentially dilutive common shares (in shares)	[2]	12,082	12,082	12,082	12,082

[1] Does not include 2.1 million shares for each of the three and nine months ended September 30, 2019 and 16.3 million shares for the three and nine months ended September 30, 2018, of unvested stock because the performance conditions had not yet been satisfied as of September 30, 2019 and 2018, respectively.

[2] In 2015, the Company issued warrants in connection with its initial public offering (the "IPO Warrants"). 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 Company 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.