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Note 5 - Financial Instruments Measured at Fair Value (Tables)

9 Months Ended

Sep. 30, 2023

Notes Tables

Unrealized Gain (Loss) on Investments [Table Text Block]

		September 30, 2023
						Gross				Gross				Estimated
		Amortized				Unrealized				Unrealized				Fair
		Cost				Gains				Losses⁽¹⁾				Value
Corporate debt securities⁽²⁾		$	40,601			$	2			$	75			$	40,528
Bank certificates of deposit			22,640				6				7				22,639
U.S. treasury securities			21,918				-				251				21,667
Asset-backed securities			8,652				-				31				8,621
Foreign government security			725				-				-				725
		$	94,536			$	8			$	364			$	94,180

		December 31, 2022
						Gross				Gross				Estimated
		Amortized				Unrealized				Unrealized				Fair
		Cost				Gains				Losses⁽¹⁾				Value
Corporate debt securities ⁽²⁾		$	59,283			$	30			$	240			$	59,073
Bank certificates of deposit			36,500				20				41				36,479
U.S. treasury securities			34,614				1				418				34,197
Asset-backed securities			12,727				10				79				12,658
Foreign government security			828				-				-				828
		$	143,952			$	61			$	778			$	143,235

Investments Classified by Contractual Maturity Date [Table Text Block]

		September 30, 2023								December 31, 2022
		Amortized				Estimated				Amortized				Estimated
		Cost				Fair Value				Cost				Fair Value
Due in one year or less		$	70,275			$	70,012			$	112,956			$	112,683
Due after one year through five years			23,536				23,443				30,996				30,552
Due after five years through ten years			725				725				-				-
		$	94,536			$	94,180			$	143,952			$	143,235

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

		Fair value measurements at September 30, 2023 using:
														Total estimated
		Level 1				Level 2				Level 3				fair value
Cash		$	243,956			$	-			$	-			$	243,956
U.S. treasury securities			-				21,667				-				21,667
Corporate debt securities			-				41,523				-				41,523
Asset-backed securities			-				8,621				-				8,621
Money market funds			-				48,435				-				48,435
Bank certificates of deposit			-				22,639				-				22,639
Foreign government security			-				725				-				725
		$	243,956			$	143,610			$	-			$	387,566

		Fair value measurements at December 31, 2022 using:
														Total estimated
		Level 1				Level 2				Level 3				fair value
Cash		$	190,371			$	-			$	-			$	190,371
Corporate debt securities			-				69,753				-				69,753
Money market funds			-				40,290				-				40,290
Bank certificates of deposit			-				37,480				-				37,480
U.S. treasury securities			-				34,196				-				34,196
Asset-backed securities			-				12,658				-				12,658
Foreign government security			-				828				-				828
		$	190,371			$	195,205			$	-			$	385,576