Note 12 - Fair Value Measurements - Summary of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Restricted cash and cash equivalents	$ 14,305		$ 12,353
Available-for-sale securities	174,121	$ 189,835
Corporate Debt Securities [Member]
Available-for-sale securities	19,905	25,778
Asset-backed Securities [Member]
Available-for-sale securities	2,456	2,480
Fair Value, Recurring [Member]
Cash and cash equivalents	112,462	147,093
Restricted cash and cash equivalents	14,305	11,409
Marketable equity securities	130,413	133,270
Total financial assets	431,301	481,607
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	87,691	92,025
Fair Value, Recurring [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	36,968
Fair Value, Recurring [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		44,249
Fair Value, Recurring [Member] \| US Treasury Securities [Member]
Available-for-sale securities	39,965	40,663
Fair Value, Recurring [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	9,497	12,898
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	112,462	147,093
Restricted cash and cash equivalents	14,305	11,409
Marketable equity securities	130,413	133,270
Total financial assets	342,785	389,207
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	45,640	56,772
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury Securities [Member]
Available-for-sale securities	39,965	40,663
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Restricted cash and cash equivalents	0	0
Marketable equity securities	0	0
Total financial assets	88,516	92,400
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	42,051	35,253
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	36,968
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		44,249
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US Treasury Securities [Member]
Available-for-sale securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	$ 9,497	$ 12,898

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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