Note 6 - Fair Value Measurements (Details Textual) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Unrealized Gain (Loss) on Securities	$ 100	$ 0
Class of Warrant or Right, Outstanding (in shares)	0

Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

No definition available.

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration