Note 10 - Fair Value Measurements - Summary of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Restricted cash and cash equivalents	$ 8,821		$ 12,134
Available-for-sale securities	149,557	$ 172,593
Corporate Debt Securities [Member]
Available-for-sale securities	64,683	67,632
Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	58,454	62,068
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	13,209	21,436
Fair Value, Recurring [Member]
Cash and cash equivalents	59,261	43,247
Restricted cash and cash equivalents	8,821	11,673
Total financial assets	373,958	367,736
Fair Value, Recurring [Member] \| Equity Securities [Member]
Available-for-sale securities	156,319	140,223
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	64,683	67,632
Fair Value, Recurring [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	58,454
Fair Value, Recurring [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		62,068
Fair Value, Recurring [Member] \| US Treasury Securities [Member]
Available-for-sale securities	13,211	21,457
Fair Value, Recurring [Member] \| US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	13,209	21,436
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	59,261	43,247
Restricted cash and cash equivalents	8,821	11,673
Total financial assets	286,553	264,521
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Equity Securities [Member]
Available-for-sale securities	156,319	140,223
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Available-for-sale securities	48,941	47,921
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	13,211	21,457
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	87,405	103,215
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	15,742	19,711
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Collateralized Mortgage Backed Securities [Member]
Available-for-sale securities	58,454
Fair Value, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member]
Available-for-sale securities		62,068
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	$ 13,209	$ 21,436

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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