Note 1 - General and Basis of Presentation - Customers as a Percentage of Total Revenues (Details) - Revenue Benchmark [Member] - Customer Concentration Risk [Member]	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Sierra Pacific Power Company And Nevada Power Company [Member]
Percent of revenues	15.40%	15.10%	17.10%	16.70%
Southern California Public Power Authority [Member]
Percent of revenues	19.50%	16.70%	19.80%	17.70%
Kenya Power and Lighting Co LTD [Member]
Percent of revenues	18.20%	18.00%	16.50%	16.60%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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