Note 6 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Nov. 13, 2014
Debt Securities, Available-for-sale, Unrealized Gain (Loss), Total	$ (200)	$ 0	$ (100)	$ 0
Class of Warrant or Right, Outstanding (in shares)	0		0
Hudson Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		818,181		818,181	58,823
Maximum [Member] | Certificates of Deposit [Member]
Marketable Securities, Realized Gain (Loss), Total		$ 100		$ 100