Note 11 - Fair Value Measurements - Summary of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Restricted cash and cash equivalents	$ 12,353		$ 8,821
Available-for-sale securities	142,040	$ 147,406
Corporate Debt Securities [Member]
Available-for-sale securities	67,478	65,653
Asset-backed Securities [Member]
Available-for-sale securities	47,682	55,185
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	12,943	13,158
Fair Value, Recurring [Member]
Cash and cash equivalents	183,765	50,334
Restricted cash and cash equivalents	12,353	10,676
Total financial assets	450,031	360,869
Fair Value, Recurring [Member] \| Equity Securities [Member]
Available-for-sale securities	111,873	152,453
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	67,478	65,653
Fair Value, Recurring [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	47,682
Fair Value, Recurring [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		55,185
Fair Value, Recurring [Member] \| US Treasury Securities [Member]
Available-for-sale securities	13,937	13,410
Fair Value, Recurring [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	12,943	13,158
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	183,765	50,334
Restricted cash and cash equivalents	12,353	10,676
Total financial assets	370,445	277,432
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Equity Securities [Member]
Available-for-sale securities	111,873	152,453
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	46,513	48,584
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	13,937	13,410
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	2,004	1,975
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	79,586	83,437
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	20,965	17,069
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	47,682
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		55,185
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	$ 10,939	$ 11,183

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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