Note 6 - Short-term Investments - Marketable Securities (Details) (Parentheticals)	Mar. 31, 2022
Deposits [Member]
Investment, interest	0.20%
Investment, maturity date	Apr. 01, 2022
Canadian Deposits [Member] \| Minimum [Member]
Investment, interest	0.50%
Investment, maturity date	Apr. 01, 2022
Canadian Deposits [Member] \| Maximum [Member]
Investment, interest	0.58%
Investment, maturity date	Mar. 30, 2023

Maturity date of investment, in YYYY-MM-DD format.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Name:	us-gaap_InvestmentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	instant