Note 1 - General and Basis of Presentation 1 (Details Textual) $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Apr. 30, 2021 USD ($)	Feb. 28, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Proceeds from Issuance of Long-term Debt, Total				$ 419,300
Proceeds from Issuance of Common Stock				339,500
Loss from Catastrophes		$ 9,100
Cash, FDIC Insured Amount			$ 29,600	18,900
Cash, Uninsured Amount			75,400	72,400
Accounts Receivable, after Allowance for Credit Loss, Current, Total			139,711	$ 149,170
Product [Member]
Revenue, Remaining Performance Obligation, Amount			$ 37,100
Revenue, Remaining Performance Obligation, Percentage			100.00%
Kenya Power and Lighting Co LTD [Member]
Accounts Receivable, Past Due			$ 47,300
Accounts Receivable, Past Due, Average Number of Days Overdue			76
Kenya Power and Lighting Co LTD [Member] | Subsequent Event [Member]
Proceeds from (Repayments of) Accounts Receivable Securitization, Total	$ 10,700
ENNE [Member]
Accounts Receivable, Past Due			$ 5,500
ENNE [Member] | Subsequent Event [Member]
Proceeds from (Repayments of) Accounts Receivable Securitization, Total	$ 2,400
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Primary Customers [Member]
Concentration Risk, Percentage			67.00%	65.00%
Non-US [Member]
Accounts Receivable, after Allowance for Credit Loss, Current, Total			$ 102,800	$ 111,300
General and Administrative Expense [Member]
Accounts Receivable, Credit Loss Expense (Reversal)			$ 3,000