Note 4 - Fair Value Measurements - Investments (Details) - USD ($) $ in Thousands		Mar. 31, 2023	Dec. 31, 2022
Adjusted cost	[1]	$ 55,169	$ 56,849
Gross unrealized losses	[1]	(19)	(16)
Fair value	[1]	55,150	56,833
Fair value	[1]	(55,150)	(56,833)
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Adjusted cost	[1]	7,622	2,143
Gross unrealized losses	[1]	0	0
Fair value	[1]	7,622	2,143
Fair value	[1]	(7,622)	(2,143)
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Adjusted cost	[1]	0	6,759
Gross unrealized losses	[1]	0	0
Fair value	[1]	0	6,759
Fair value	[1]	0	(6,759)
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Adjusted cost	[1]	47,547	47,947
Gross unrealized losses	[1]	(19)	(16)
Fair value	[1]	47,528	47,931
Fair value	[1]	$ (47,528)	$ (47,931)

[1] FASB Topic 820, Fair Value Measurements, establishes a fair value hierarchy that requires the use of observable market data, when available, and prioritizes the inputs to valuation techniques used to measure fair value in the following categories: Level 1: Quoted market prices in active markets for identical assets or liabilities. Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data. Level 3: Unobservable inputs that are not corroborated by market data.