Note 2 - Summary of Significant Accounting Policies - Securities that Potentially Dilute Calculation of Diluted Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Antidilutive securities (in shares)	1,552,813	1,800,150	60,512
Warrants to Purchase Common Stock - Liability Classified [Member]
Antidilutive securities (in shares)	55,963	359,619	55,119
Warrants to Purchase Common Stock - Equity Classified [Member]
Antidilutive securities (in shares)	6	70	70
Convertible 2017 Notes [Member]
Antidilutive securities (in shares)			3,756
Convertible 2020 Notes [Member]
Antidilutive securities (in shares)	1,071,674	1,437,984
Convertible 2022 Notes [Member]
Antidilutive securities (in shares)			280
Employee Stock Option [Member]
Antidilutive securities (in shares)	2,311	2,322	846
Restricted Stock [Member]
Antidilutive securities (in shares)	290,300	155	441
Stock Appreciation Rights (SARs) [Member]
Antidilutive securities (in shares)	132,559