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Accounts receivable
12 Months Ended
Dec. 31, 2017
Receivables [Abstract]  
Accounts receivable
Accounts receivable
 
 
December 31, 2017

 
December 31, 2016

Trade
 
$
45,158

 
$
38,746

Holdbacks
 
558

 
528

Other
 
1,512

 
806

 
 
$
47,228

 
$
40,080


Holdbacks represent amounts up to 10% of the contract value under certain contracts that the customer is contractually entitled to withhold until completion of the project or until certain project milestones are achieved.