Note 5 - Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2020

Notes Tables

Schedule of Available-for-sale Securities Reconciliation [Table Text Block]

	June 30, 2020 (Unaudited)
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Available-for-sale - matures within one year:
Corporate bonds	$	16,772	$	62	$	(27	)	$	16,807
		16,772		62		(27	)		16,807
Available-for-sale - matures after one year through five years:
Corporate bonds		50,272		547		(333	)		50,486
		50,272		547		(333	)		50,486
Total	$	67,044	$	609	$	(360	)	$	67,293

	December 31, 2019
	Amortized cost		Gross unrealized gains		Gross unrealized losses			Fair value
Available-for-sale - matures within one year:
Corporate bonds	$	18,224	$	16	$	(11	)	$	18,229
		18,224		16		(11	)		18,229
Available-for-sale - matures after one year through five years:
Corporate bonds		46,593		168		(123	)		46,638
		46,593		168		(123	)		46,638
Total	$	64,817	$	184	$	(134	)	$	64,867

Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block]

	Less than 12 months					12 months or greater
	Fair value		Gross unrealized loss			Fair value		Gross unrealized loss
As of June 30, 2020 (unaudited)	$	28,365	$	(340	)	$	2,974	$	(20	)
As of December 31, 2019	$	22,852	$	(102	)	$	14,231	$	(32	)

Schedule of Realized Gain (Loss) [Table Text Block]

	Six months ended June 30,						Three months ended June 30,
	2020			2019			2020			2019
	(unaudited)			(unaudited)			(unaudited)			(unaudited)
Gross realized gains from sale of available-for-sale marketable securities	$	4		$	—		$	—		$	—
Gross realized losses from sale of available-for-sale marketable securities	$	(19	)	$	(35	)	$	(13	)	$	(11	)