Note 3 - Investments and Fair Value Measurements - Summary of Unaudited Financial Statements of Affiliate (Details) (Parentheticals)	Dec. 31, 2019	Jun. 30, 2019	Mar. 30, 2019
Virtual Power Systems [Member]
Ownership Percentage	20.58%	20.58%	21.40%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant