Note 4 - Financial Statement Details (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Proceeds from Coronavirus Economic Relief for Transportation Services (CERTS) Act, Grant	$ 21,000
Other Nonoperating Income (Expense), Total		$ 4,357	$ (74)	$ 4,362	$ (188)
Financing Receivable, Credit Loss, Expense (Reversal)		0		0
Grant [Member]
Other Nonoperating Income (Expense), Total		$ 4,400		$ 4,400