Note 3 - Fair Value Measurements (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2019

Dec. 31, 2018

Notes Tables

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

	As of September 30, 2019
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	9,101	$	-	$	-	$	9,101
Total	$	9,101	$	-	$	-	$	9,101

	As of December 31, 2018
	Quoted Prices in Active Markets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Assets
Cash equivalents	$	18,353	$	-	$	-	$	18,353
Government securities		2,496		-		-		2,496
Total	$	20,849	$	-	$	-	$	20,849

	As of December 31, 2018
	Quoted Prices		Significant		Significant
	in Active		Observable		Unobservable
	Markets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Total
Assets
Cash equivalents	$	18,353	$	-	$	-	$	18,353
Government securities		2,496		-		-		2,496
Total	$	20,849	$	-	$	-	$	20,849

	As of December 31, 2017
	Quoted Prices		Significant		Significant
	in Active		Observable		Unobservable
	Markets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Total
Assets
Cash equivalents	$	11,662	$	-	$	-	$	11,662
Government securities		20,971		-		-		20,971
Total	$	32,633	$	-	$	-	$	32,633

Available-for-sale Securities [Table Text Block]

	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
September 30, 2019
Government securities
(Due within 1 year)	$	-	$	-	$	-	$	-
	$	-	$	-	$	-	$	-
December 31, 2018
Government securities
(Due within 1 year)	$	2,496	$	-	$	-	$	2,496
	$	2,496	$	-	$	-	$	2,496

	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
December 31, 2018
Government securities
(Due within 1 year)	$	2,496	$	-	$	-		$	2,496
	$	2,496	$	-	$	-		$	2,496
December 31, 2017
Government securities
(Due within 1 year)	$	20,991	$	-	$	(20	)	$	20,971
	$	20,991	$	-	$	(20	)	$	20,971