Note 10 - Fair Value Measurements - Summary of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Restricted cash and cash equivalents	$ 14,688		$ 16,505
Available-for-sale securities	147,811	$ 147,406
Corporate Debt Securities [Member]
Available-for-sale securities	67,151	65,653
Asset-backed Securities [Member]
Available-for-sale securities	53,465	55,185
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	13,065	13,158
Fair Value, Recurring [Member]
Cash and cash equivalents	69,492	50,334
Restricted cash and cash equivalents	14,688	10,676
Total financial assets	324,052	360,869
Fair Value, Recurring [Member] \| Equity Securities [Member]
Available-for-sale securities	92,061	152,453
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	67,151	65,653
Fair Value, Recurring [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	53,465
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	14,130	13,410
Fair Value, Recurring [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	13,065	13,158
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	69,492	50,334
Restricted cash and cash equivalents	14,688	10,676
Total financial assets	239,779	277,432
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Equity Securities [Member]
Available-for-sale securities	92,061	152,453
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	47,434	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	14,130	13,410
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	1,974	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	84,273	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	19,717	17,069
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	53,465
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	$ 11,091	$ 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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