Note 9 - Fair Value Measurement (Details Textual) $ in Thousands	3 Months Ended
Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)
Payments to Acquire Equity Securities, FV-NI	$ 10,868	$ (0)
Proceeds from Sale of Equity Securities, FV-NI	2,487	0
Senior Notes [Member]
Notes Payable, Total	469,700
Senior Notes [Member] \| Fair Value, Inputs, Level 1 [Member]
Notes Payable, Fair Value Disclosure	498,500
Senior Notes [Member] \| IQ Notes [Member]
Notes Payable, Total	39,200
Senior Notes [Member] \| IQ Notes [Member] \| Fair Value, Inputs, Level 3 [Member]
Notes Payable, Fair Value Disclosure	$ 40,500
Senior Notes [Member] \| IQ Notes [Member] \| Fair Value, Inputs, Level 3 [Member] \| Measurement Input, Annual Yield [Member]
Debt Instrument, Measurement Input	6
Equity Securities in Mining Companies [Member]
Payments to Acquire Equity Securities, FV-NI	$ 10,900	0
Equity Securities, FV-NI, Cost	2,400
Proceeds from Sale of Equity Securities, FV-NI	$ 2,500	$ 0

Value of input used to measure debt instrument, including, but not limited to, convertible and non-convertible debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Fair value portion of notes payable.

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Amount of cash outflow to acquire investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as investing activity.

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Amount of cash inflow from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as investing activity.

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