Note 10 - Stockholders' Equity (Details Textual)											1 Months Ended		6 Months Ended	9 Months Ended	28 Months Ended	55 Months Ended	56 Months Ended
	Oct. 04, 2017 USD ($)	Jul. 06, 2017 USD ($) $ / shares shares	Jun. 26, 2017 USD ($) $ / shares shares	Jun. 09, 2017 USD ($) $ / shares shares	May 26, 2017	Feb. 14, 2017 USD ($) $ / shares shares	Dec. 20, 2016 USD ($) $ / shares shares	Jun. 13, 2016 USD ($) $ / shares shares	Oct. 02, 2015 USD ($)	Feb. 01, 2013 USD ($)	Sep. 30, 2015 USD ($)	Feb. 25, 2013 USD ($)	Jun. 30, 2017 USD ($) shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	May 16, 2017 shares	May 15, 2017 shares	Dec. 31, 2016 $ / shares shares	Jun. 30, 2016 shares	May 31, 2016 shares	May 27, 2015 $ / shares shares	Jan. 15, 2014 $ / shares shares	Feb. 22, 2013 $ / shares shares
Shelf Registration Statement Amount | $											$ 75,000,000
Common Stock, Shares Authorized														112,500,000	112,500,000	112,500,000	112,500,000			112,500,000	112,500,000	75,000,000
Preferred Stock, Shares Authorized														100,000	100,000	100,000	100,000			100,000	100,000
Aggregate of Common and Preferred Stock, Shares Authorized																					112,600,000
Common Stock, Shares, Outstanding														8,354,679	8,354,679	8,354,679	8,354,679	4,070,172	56,982,418	2,230,118
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number														679,752	679,752	679,752	679,752	200,000	2,400,000	210,023
Class of Warrant or Right, Outstanding														5,528,634	5,528,634	5,528,634	5,528,634	2,400,000	33,500,000	1,487,958
Class of Warrant or Right, Number of Securities Called by Warrants or Rights			506,627	790,410
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares			$ 1.65	$ 2.70										$ 5.33	$ 5.33	$ 5.33	$ 5.33			$ 9.39
Proceeds from Warrant Exercises | $															$ 800,000	$ 2,100,000
Common Stock, Par or Stated Value Per Share | $ / shares														$ 0.01	$ 0.01	$ 0.01	$ 0.01			$ 0.01
Aggregate Offering Price, Additions | $									$ 7,500,000
2013 Warrants, 2014 Warrants, and June 2016 Warrants [Member]
Increase (Decrease) in Fair Value of Warrants | $				$ 200,000
2015 Warrants [Member]
Increase (Decrease) in Fair Value of Warrants | $			$ 100,000
July 2017 Direct Offering [Member]
Stock Issued During Period, Shares, New Issues		2,050,000
Share Price | $ / shares		$ 2.07
Proceeds from Issuance of Common Stock, Gross | $		$ 4,243,500
July 2017 Direct Offering [Member] | Pre-Funded Series CCC Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		385,000
Beneficial Ownership Percentage Threshold		9.99%
Class of Warrant or Right, Offered Price of Warrants or Rights | $ / shares		$ 2.06
Proceeds from Issuance of Warrants | $		$ 793,100
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares		$ 0.01
Class of Warrant or Right, Exercised During Period														385,000
July 2017 Direct Offering [Member] | Series AAA Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		2,435,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares		$ 2.07
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right		1
Class of Warrant or Right, Exercisable Period		180 days
Warrants Issued, Expiration Period		5 years 182 days
July 2017 Direct Offering [Member] | Series BBB Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		2,435,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares		$ 4.75
Warrants Issued, Expiration Period		1 year
July 2017 Direct Offering [Member] | Series AAA and Series BBB Warrants [Member] | Subsequent Event [Member]
Proceeds from Issuance of Warrants | $	$ 16.60
February 14, 2017 Public Offering [Member]
Stock Issued During Period, Shares, New Issues						1,384,704
Shares Issued, Price Per Share | $ / shares						$ 3.22
Maximum Beneficial Ownership of the Purchaser						9.99%
Proceeds from Issuance of Common Stock | $						$ 5,000,000
February 14, 2017 Public Offering [Member] | Series AA Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						1,177,790
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 3.22
Class of Warrant or Right, Term						5 years
Stock Issued During Period, Shares, Exercise of Warrants													638,809
Proceeds from Warrant Exercises | $													$ 2,100,000
February 14, 2017 Public Offering [Member] | Pre-Funded Series BB Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						185,713
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 0.14
Shares Issued, Price Per Share | $ / shares						$ 3.08
Stock Issued During Period, Shares, Exercise of Warrants														185,713
December 2016 Common Stock Offering [Member]
Stock Issued During Period, Shares, New Issues							367,346
Share Price | $ / shares							$ 4.90
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							367,343
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares							$ 6.44
Warrants Issued, Expiration Period							5 years 182 days
Proceeds from Issuance of Common Stock | $							$ 1,800,000
Warrants Exercisable Period							180 days
June 2016 Common Stock Offering [Member]
Stock Issued During Period, Shares, New Issues								165,126
Share Price | $ / shares								$ 19.04
Class of Warrant or Right, Number of Securities Called by Warrants or Rights								630,252
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares								$ 19.60
Proceeds from Issuance of Common Stock | $								$ 6,000,000
Common Stock, Par or Stated Value Per Share | $ / shares								$ 0.01
June 2016 Common Stock Offering [Member] | Series A Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right								0.5
Warrants Issued, Expiration Period								5 years 182 days
Warrants Exercisable Period								180 days
June 2016 Common Stock Offering [Member] | Series C Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right								1
Warrants Issued, Expiration Period								1 year
Warrants Exercisable Period								180 days
June 2016 Common Stock Offering [Member] | Series D Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right								0.5
Warrants Issued, Expiration Period								5 years 182 days
Warrants Exercisable Period								180 days
February 2013 Preferred Stock Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights																									95,811
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares																									$ 74.34
January 2014 Common Stock Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights																								64,348
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares																								$ 57.40
May 2015 Common Stock Offering [Member] | 2015 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights																							139,284
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares																							$ 36.40
ATM Agreement [Member]
Stock Issued During Period, Shares, New Issues																	105,678
Proceeds from Issuance of Common Stock | $																	$ 7,600,000
Aggregate Offering Price | $										$ 25,000,000				$ 17,400,000
Commission on Proceeds from ATM Shares Percent												3.00%
Legal Fees | $												$ 50,000
Aggregate Offering Price, Additions | $									$ 7,500,000
Reverse Stock Split [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio					14