Note 6 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2021

Notes Tables

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

			Fair Value Measurements Using
			Quoted Prices		Significant
			in Active		Other
	Balance as of		Markets for		Observable
	December 31,		Identical Assets		Inputs
	2021		(Level 1)		(Level 2)
Marketable securities:
US government	$	19,307	$	19,307	$	—
Corporate bonds		8,652		—		8,652
Commercial paper		14,492		—		14,492
Money market funds(1)		21,402		21,402		—
Certificates of deposit		3,003		—		3,003
Total marketable securities	$	66,856	$	40,709	$	26,147

			Fair Value Measurements Using
			Quoted Prices		Significant
			in Active		Other
	Balance as of		Markets for		Observable
	December 31,		Identical Assets		Inputs
	2020		(Level 1)		(Level 2)
Marketable securities:
US government	$	29,186	$	29,186	$	—
Corporate bonds		21,861		—		21,861
Money market funds(1)		39,744		39,744		—
Total marketable securities	$	90,791	$	68,930	$	21,861