Note 11 - Fair Value Measurements - Summary of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Restricted cash and cash equivalents	$ 21,984		$ 14,688
Available-for-sale securities	189,175	$ 189,835
Corporate Debt Securities [Member]
Available-for-sale securities	26,420	25,778
Asset-backed Securities [Member]
Available-for-sale securities	3,949	2,480
Fair Value, Recurring [Member]
Cash and cash equivalents	134,107	147,093
Restricted cash and cash equivalents	21,984	11,409
Total financial assets	485,595	481,607
Fair Value, Recurring [Member] \| Equity Securities [Member]
Available-for-sale securities	140,329	133,270
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	93,625	92,025
Fair Value, Recurring [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	43,089
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	41,364	40,663
Fair Value, Recurring [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	11,097	12,898
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	134,107	147,093
Restricted cash and cash equivalents	21,984	11,409
Total financial assets	389,745	389,207
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Equity Securities [Member]
Available-for-sale securities	140,329	133,270
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	51,961	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	41,364	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
Total financial assets	95,850	92,400
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Equity Securities [Member]
Available-for-sale securities	0	0
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	41,664	35,253
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	43,089
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	$ 11,097	$ 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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