Note 3 - Trade Accounts Receivable - Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance—beginning of year	$ 3,482	$ 2,952	$ 2,224
Provision for bad debts	1,044	530	728
Charge-offs	0	0	0
Recoveries	0	0	0
Balance—end of year	$ 4,526	$ 3,482	$ 2,952