Note 3 - Trade Accounts Receivable - Accounts Receivable Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Billed	$ 57,495	$ 56,766
Unbilled	7,241	8,808
Allowance for doubtful accounts	(2,952)	(2,224)	$ (1,335)	$ (994)
Total accounts receivable—net	$ 61,784	$ 63,350

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

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