Note 5 - Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

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

			Fair Value Measurements at Reporting Date Using
	June 30, 2019		Quoted Prices in Active Markets for Identical Assets  (Level 1)		Significant Other Observable Inputs  (Level 2)		Significant  Unobservable Inputs  (Level 3)		Amortized Cost
Cash equivalents:
Money market funds	$	1,305	$	1,305	$	-	$	-	$	1,305
Investments:
U.S. treasury bills	$	72,045	$	72,045	$	-	$	-	$	72,032

			Fair Value Measurements at Reporting Date Using
	December 31, 2018		Quoted Prices in Active Markets for Identical Assets  (Level 1)		Significant Other Observable Inputs  (Level 2)		Significant  Unobservable Inputs  (Level 3)		Amortized Cost
Cash equivalents:
Money market funds	$	4,984	$	4,984	$	-	$	-	$	4,984
Investments:
U.S. treasury bills	$	69,972	$	69,972	$	-	$	-	$	69,972