Note 10 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares shares in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Potentially dilutive common shares (in shares)		31,778	29,550	31,433	27,255
Unvested Stock [Member]
Potentially dilutive common shares (in shares)	[1]	848	989	993	768
Convertible Preferred Stocks [Member]
Potentially dilutive common shares (in shares)		16,869	14,678	16,386	12,829
Common Stock Warrants [Member]
Potentially dilutive common shares (in shares)		1,979	1,801	1,972	1,576
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 nine months ended September 30, 2020 and 3.2 million shares for the three and nine months ended September 30, 2019, of unvested stock because the performance conditions had not yet been satisfied as of September 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.