Note 14 - Subsequent Events (Details Textual) - USD ($)		1 Months Ended	2 Months Ended	12 Months Ended
	Feb. 12, 2018	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Proceeds from Issuance of Common Stock				$ 31,565,000	$ 13,886,000
November 2017 ATM Facility [Member]
Stock Issued During Period, Shares, New Issues			59,249
Proceeds From Issuance of Common Stock, Net			$ 125,000
Subsequent Event [Member] | February 2018 Offering [Member]
Stock Issued During Period, Shares, New Issues	11,500,000
Share Price	$ 3
Proceeds from Issuance of Common Stock	$ 34,500,000
Proceeds From Issuance of Common Stock, Net	$ 32,380,000
Subsequent Event [Member] | November 2017 ATM Facility [Member]
Stock Issued During Period, Shares, New Issues		208,277
Proceeds From Issuance of Common Stock, Net		$ 1,025,000