Note 3 - Trade Accounts Receivable - Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance—beginning of year	$ 2,224	$ 1,335	$ 994
Provision for bad debts	728	889	341
Charge-offs
Recoveries
Balance—end of year	$ 2,952	$ 2,224	$ 1,335