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Note 3 - Trade Accounts Receivable - Accounts Receivable Balances (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Billed $ 56,766 $ 51,236    
Unbilled 8,808 9,154    
Allowance for doubtful accounts (2,224) (1,335) $ (994) $ (549)
Total accounts receivable—net $ 63,350 $ 59,055