Note 1 - General and Basis of Presentation 1 (Details Textual) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 27, 2022 USD ($)	Jun. 22, 2022 USD ($) $ / shares shares	Apr. 12, 2022 USD ($)	Jul. 31, 2022 USD ($)	Jun. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) $ / shares	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) $ / shares
Proceeds from Notes Payable, Total							$ 420,400	$ 0
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares		$ 0.001			$ 0.001		$ 0.001		$ 0.001
Purchase of Capped Call Instruments							$ 24,538	(0)
Payments for Repurchase of Common Stock					$ 18,000		17,964	(0)
Treasury Stock, Shares, Acquired (in shares) | shares					258,667
Treasury Stock Acquired, Average Cost Per Share (in dollars per share) | $ / shares					$ 69.45
Repayments of Long-Term Debt, Total							96,875	36,481
Exploration Abandonment and Impairment Expense					$ 0	$ 0	0	$ 0
Cash, FDIC Insured Amount					36,300		36,300		$ 31,000
Cash, Uninsured Amount					55,700		55,700		64,300
Accounts Receivable, after Allowance for Credit Loss, Current, Total					123,398		123,398		$ 122,944
Kenya Power and Lighting Co Limited [Member]
Accounts Receivable, Past Due					27,200		27,200
Kenya Power and Lighting Co Limited [Member] | Subsequent Event [Member]
Proceeds, Overdue Accounts Receivable				$ 9,600
ENEE [Member]
Accounts Receivable, Past Due					21,400		$ 21,400
ENEE [Member] | Subsequent Event [Member]
Proceeds, Overdue Accounts Receivable				$ 900
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Primary Customers [Member]
Concentration Risk, Percentage							51.00%		58.00%
Non-US [Member]
Accounts Receivable, after Allowance for Credit Loss, Current, Total					82,900		$ 82,900		$ 77,500
Fire [Member]
Insurance Recoveries					4,000
Increase (Decrease) in Insurance Settlements Receivable					(600)
Gain on Business Interruption Insurance Recovery					3,400
Senior Unsecured Bonds, Series 3 [Member]
Repayments of Long-Term Debt, Total	$ 221,900
Extinguishment of Debt, Amount	218,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities, Total	2,800
Debt Instrument, Unamortized Premium, Total	1,100
Mizrahi Loan Agreement [Member]
Debt Instrument, Face Amount			$ 75,000
Debt Instrument, Interest Rate, Stated Percentage			4.10%
Debt Instrument, Number of Payments			16
Debt Instrument, Periodic Payment, Total			$ 4,700
Debt Instrument, Date of First Required Payment			Oct. 12, 2022
Debt Instrument, Term (Year)			8 years
Debt Instrument, Covenant, Debt to Adjusted EBITDA Ratio			6.00%
Debt Instrument, Covenant, Minimum Equity Capital			$ 750,000
Debt Instrument, Covenant, Equity Capital to Total Assets Ratio			25.00%
Call Option [Member]
Option Indexed to Issuer's Equity, Shares (in shares) | shares		4,800,000
Option Indexed to Issuer's Equity, Strike Price (in dollars per share) | $ / shares		$ 90.27
Option Indexed to Issuer's Equity, Cap Price		107.63%
Option Indexed to Issuer's Equity, Premium Percentage		55.00%
Purchase of Capped Call Instruments					24,500
Convertible Senior Notes [Member]
Debt Instrument, Face Amount	431,250	$ 375,000
Debt Instrument, Interest Rate, Stated Percentage		2.50%
Proceeds from Notes Payable, Total	$ 56,250
Debt Instrument, Convertible, Threshold Trading Days		20
Debt Instrument, Convertible, Threshold Consecutive Trading Days		30
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger		130.00%
Debt Instrument, Convertible, Conversion Price (in dollars per share) | $ / shares		$ 90.27
Debt Instrument, Convertible, Threshold Trading Days, Measurement Period Request (Year)		5 years
Debt Instrument, Convertible, Maximum Percentage of Stock Price Trigger Per $1000		98.00%
Debt Instrument, Convertible, Conversion Shares Per $1000		11.0776
Debt Instrument, Redemption Price, Percentage		100.00%
Debt Instrument, Cumulative Sinking Fund Payments		$ 0
Debt Issuance Costs, Gross		$ 10,900
Amortization of Debt Issuance Costs					$ 18,000		$ 18,000
Debt Instrument, Interest Rate, Effective Percentage					3.10%		3.10%