Note 11 - Stock Based Compensation (Details) - Summary of Stock Option Awards and Changes - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number (in Shares)	2,139,822	1,744,755	861,905	725,529
Options Outstanding, Weighted Average Exercise Price	$ 5.64	$ 7.20	$ 12.30	$ 14.63
Options Exercisable, Number (in Shares)	1,315,201
Options Exercisable,Weighted Average Remaining Contractual Term (in years)	6 years 6 months
Range 1 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range	$ 1.00
Range of Exercise Prices, Upper Range	$ 2.99
Options Outstanding, Number (in Shares)	725,166
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	9 years 146 days
Options Outstanding, Weighted Average Exercise Price	$ 2.33
Options Exercisable, Number (in Shares)	161,867
Options Exercisable,Weighted Average Remaining Contractual Term (in years)	9 years 73 days
Options Exercisable, Weighted Average Exercise Price	$ 2.44
Range 2 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range	3.00
Range of Exercise Prices, Upper Range	$ 5.99
Options Outstanding, Number (in Shares)	915,195
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	8 years 109 days
Options Outstanding, Weighted Average Exercise Price	$ 3.99
Options Exercisable, Number (in Shares)	653,873
Options Exercisable,Weighted Average Remaining Contractual Term (in years)	7 years 328 days
Options Exercisable, Weighted Average Exercise Price	$ 3.75
Range 3 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range	6.00
Range of Exercise Prices, Upper Range	$ 12.99
Options Outstanding, Number (in Shares)	337,183
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years
Options Outstanding, Weighted Average Exercise Price	$ 10.84
Options Exercisable, Number (in Shares)	337,183
Options Exercisable,Weighted Average Remaining Contractual Term (in years)	4 years
Options Exercisable, Weighted Average Exercise Price	$ 10.82
Range 4 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Lower Range	13.00
Range of Exercise Prices, Upper Range	$ 19.99
Options Outstanding, Number (in Shares)	92,414
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 109 days
Options Outstanding, Weighted Average Exercise Price	$ 14.36
Options Exercisable, Number (in Shares)	92,414
Options Exercisable,Weighted Average Remaining Contractual Term (in years)	4 years 109 days
Options Exercisable, Weighted Average Exercise Price	$ 14.36
Range 5 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number (in Shares)	69,864
Options Outstanding, Weighted Average Remaining Contractual Term (in years)	2 years 73 days
Options Outstanding, Weighted Average Exercise Price	$ 24.85
Options Exercisable, Number (in Shares)	69,864
Options Exercisable,Weighted Average Remaining Contractual Term (in years)	2 years 73 days
Options Exercisable, Weighted Average Exercise Price	$ 24.85