Note 10 - Stockholders' Equity (Details) - Waived Warrants - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 28, 2013	Jun. 03, 2013	Dec. 31, 2012
Class of Warrant or Right [Line Items]
Shares of common stock associated with waived warrants (in Shares)	5,894,675	5,069,815	3,170,520			1,747,478
Strike price	$ 6.37	$ 8.18	$ 10.65			$ 15.17
Per share fair value	$ 6.37	$ 8.18	$ 10.65			$ 15.17
February 26, 2018 [Member]
Class of Warrant or Right [Line Items]
Shares of common stock associated with waived warrants (in Shares)	1,323,496
Expiration date of waived warrants	Feb. 26, 2018
Strike price	$ 5.31
Per share fair value	$ 5.31
July 25, 2016 [Member]
Class of Warrant or Right [Line Items]
Shares of common stock associated with waived warrants (in Shares)	31,243
Expiration date of waived warrants	Jul. 25, 2016
Strike price	$ 18.99
Per share fair value	$ 18.99
July 6, 2016 [Member]
Class of Warrant or Right [Line Items]
Shares of common stock associated with waived warrants (in Shares)	12,628
Expiration date of waived warrants	Jul. 06, 2016
Strike price	$ 14.09
Per share fair value	$ 14.09
November 25, 2017 [Member]
Class of Warrant or Right [Line Items]
Shares of common stock associated with waived warrants (in Shares)	31,448
Expiration date of waived warrants	Nov. 25, 2017
Strike price	$ 12.47
Per share fair value	$ 12.47
Estimate of Fair Value Measurement [Member] | February 26, 2018 [Member]
Class of Warrant or Right [Line Items]
Strike price				$ 3.86	$ 6.60
Per share fair value				3.86	6.60
Estimate of Fair Value Measurement [Member] | July 25, 2016 [Member]
Class of Warrant or Right [Line Items]
Strike price				2.10	4.41
Per share fair value				2.10	4.41
Estimate of Fair Value Measurement [Member] | July 6, 2016 [Member]
Class of Warrant or Right [Line Items]
Strike price				2.40	4.81
Per share fair value				2.40	4.81
Estimate of Fair Value Measurement [Member] | November 25, 2017 [Member]
Class of Warrant or Right [Line Items]
Strike price				3.16	5.56
Per share fair value				$ 3.16	$ 5.56