Note 4 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2022

Notes Tables

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	Fair Value Measurements as of December 31, 2022 (000's):
	Quoted Prices		Significant
	in Active		Other		Significant
	Markets for		Observable		Unobservable
	Identical Assets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Fair Value
Assets
Corporate bonds	$	—	$	87,760	$	—	$	87,760
Commercial paper		37,682		—		—		37,682
Certificates of deposit		—		19,667		—		19,667
Asset-backed securities		—		6,554		—		6,554
Money market funds (cash equivalents)		9,438		—		—		9,438
Total assets	$	47,120	$	113,981	$	—	$	161,101

	Fair Value Measurements as of December 31, 2021 (000's):
	Quoted Prices		Significant
	in Active		Other		Significant
	Markets for		Observable		Unobservable
	Identical Assets		Inputs		Inputs
	(Level 1)		(Level 2)		(Level 3)		Fair Value
Assets
Money market funds (cash equivalents)	$	130,005	$	—	$	—	$	130,005
Total assets	$	130,005	$	—	$	—	$	130,005