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Note 2 - Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

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
December 31, 2017
Available-for-sale securities:
Corporate bonds and notes		$	8,458			$	19			$	(49	)		$	8,428
Municipal bonds			4,637				1				(28	)			4,610
Total available-for-sale securities		$	13,095			$	20			$	(77	)		$	13,038

December 31, 2016
Available-for-sale securities:
Corporate bonds and notes		$	20,028			$	64			$	(122	)		$	19,970
Municipal bonds			6,463				6				(44	)			6,425
Total available-for-sale securities		$	26,491			$	70			$	(166	)		$	26,395

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

		Amortized				Estimated
		cost				fair value

Due within one year		$	2,688			$	2,688
Due after one year through five years			10,408				10,350
Total available-for-sale securities		$	13,096			$	13,038

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 December 31, 2017
Corporate bonds and notes		$	3,799			$	(20	)			2,125			$	(30	)		$	5,924			$	(50	)
Municipal bonds			3,341				(18	)			657				(9	)			3,998				(27	)
		$	7,140			$	(38	)		$	2,782			$	(39	)		$	9,922			$	(77	)