Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Marketable Securities [Table Text Block]

	December 31, 2019
	Amortized cost		Gross unrealized gain		Gross unrealized loss			Fair value
Matures within one year:
Corporate debentures	$	27,624	$	24	$	(11	)	$	27,637
Government debentures		4,930		-		-			4,930
		32,554		24		(11	)		32,567
Matures after one year through three years:
Corporate debentures		91,887		575		(117	)		92,345
Government debentures		3,030		21		(3	)		3,048
		94,917		596		(120	)		95,393
Total	$	127,471	$	620	$	(131	)	$	127,960
	December 31, 2018
	Amortized cost		Gross unrealized gain		Gross unrealized loss			Fair value
Matures within one year:
Corporate debentures	$	3,999	$	-	$	(18	)	$	3,981
		3,999		-		(18	)		3,981
Matures after one year through three years:
Corporate debentures		33,698		29		(346	)		33,381
Government debentures		11,360		-		(138	)		11,222
		45,058		29		(484	)		44,603
Total	$	49,057	$	29	$	(502	)	$	48,584

Schedule of Unrealized Loss on Investments [Table Text Block]

	December 31, 2019
	Less than 12 months					12 months or greater					Total
	Fair value		Unrealized Losses			Fair value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debentures	$	57,753	$	(127	)	$	3,801	$	(1	)	$	61,554	$	(128	)
Government debentures		2,552		(3	)		-		-			2,552		(3	)
Total	$	60,305	$	(130	)	$	3,801	$	(1	)	$	64,106	$	(131	)

	December 31, 2018
	Less than 12 months					12 months or greater					Total
	Fair value		Unrealized Losses			Fair value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debentures	$	12,017	$	(126	)	$	16,547	$	(238	)	$	28,564	$	(364	)
Government debentures		8,864		(117	)		2,357		(21	)		11,221		(138	)
Total	$	20,881	$	(243	)	$	18,904	$	(259	)	$	39,785	$	(502	)

Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block]

	December 31, 2019
	Level 1		Level 2		Level 3		Total
Assets:
Marketable securities	$	-	$	127,960	$	-	$	127,960
Foreign currency derivative contracts		-		16		-		16
Total financial assets	$	-	$	127,976	$	-	$	127,976
	December 31, 2018
	Level 1		Level 2		Level 3		Total
Assets:
Marketable securities	$	-	$	48,584	$	-	$	48,584
Total financial assets	$	-	$	48,584	$	-	$	48,584
Liabilities:
Foreign currency derivative contracts	$	-	$	111	$	-	$	111
Total financial liabilities	$	-	$	111	$	-	$	111