Note 5 - Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2019

Notes Tables

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

			Fair Value Measurements at Reporting Date Using
	March 31, 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	$	2,147	$	2,147	$	–	$	–	$	2,147
Investments:
U.S. treasury bills	$	71,221	$	71,221	$	–	$	–	$	71,221

			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