Note 4 - Accounts Receivable, Transit Accounts Receivable and Transit Accounts Payable - Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 30, 2017
Allowance for sales discounts and doubtful accounts	$ (1,116)	$ (967)
Accounts receivable, net	51,913	46,080
Billed Revenues [Member]
Accounts receivable, current	33,405	31,448
Unbilled Revenues [Member]
Accounts receivable, current	14,446	10,573
Work In Progress [Member]
Accounts receivable, current	$ 5,178	$ 5,026

Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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