Note 4 - Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

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

	Amortized cost		Gross unrealized holding gains		Gross unrealized holding losses			Estimated fair value
June 30 , 2019
Available-for-sale securities:
Corporate bonds and notes	$	5,756	$	96	$	(7	)	$	5,845
Municipal bonds		4,082		20		(1	)		4,101
Total available-for-sale securities	$	9,838	$	116	$	(8	)	$	9,946
December 31, 2018
Available-for-sale securities:
Corporate bonds and notes	$	2,911	$	1	$	(31	)	$	2,881
Municipal bonds		1,849		—		(15	)		1,834
Total available-for-sale securities	$	4,760	$	1	$	(46	)	$	4,715

Available-for-sale Securities, Debt Maturities [Table Text Block]

	Amortized cost		Estimated fair value
Due within one year	$	3,081	$	3,092
Due after one year through five years		6,757		6,854
Due after five years		—		—
Total available-for-sale securities	$	9,838	$	9,946

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

	Less than 12 months					More than 12 months					Total
	Estimated fair value		Gross unrealized holding losses			Estimated fair value		Gross unrealized holding losses			Estimated fair value		Gross unrealized holding losses
As of June 30 , 2019
Corporate bonds and notes	$	293	$	(5	)	$	562	$	(2	)	$	855	$	(7	)
Municipal bonds		—		—			690		(1	)		690		(1	)
Total	$	293	$	(5	)	$	1,252	$	(8	)	$	1,545	$	(8	)