Note 12 - Warrants and Derivative Liabilities (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
	Nov. 13, 2019	Apr. 17, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Mar. 31, 2019	Nov. 13, 2014
Class of Warrant or Right, Outstanding (in shares)			0		0
Gain (Loss) in Change of Fair Value of Derivative Instruments and Warrants, Net of Tax				$ 1,145		$ 4,092
Hercules Warrants [Member]
Gain (Loss) on Decrease Fair Value Upon Exercise of Warrant					$ 100
November 2014 Warrant [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 7.81								$ 7.81
Common Unit, Issued (in shares)									909,090
Common Shares Per Unit (in shares)									1
Class of Warrant or Right, Number of Warrants to Purchase One Share of Stock (in shares)									0.9
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)									818,181
Class of Warrant or Right, Warrants Exercised (in shares)	786,000
Class of Warrant or Right, Warrants Expired (in shares)	32,181
Gain (Loss) in Change of Fair Value of Derivative Instruments and Warrants, Net of Tax				$ 1,100		$ 4,100
Hercules Technology Growth Capital [Member]
Stock Issued During Period, Shares, Warrant Exercised (in shares)		22,821
Secured Debt [Member] | Hercules Technology Growth Capital [Member] | Hercules Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)							$ 7.85
Derivative, Fair Value, Net, Total								$ 400