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

4.  Accounts Receivable

 

 

 

December 31,

 

 

 

2017

 

 

2016

 

 

 

(In Thousands)

 

Trade receivables and other

 

$

59,873

 

 

$

51,656

 

Allowance for doubtful accounts

 

 

(303

)

 

 

(357

)

 

 

$

59,570

 

 

$

51,299

 

 

Sales to our customers are generally unsecured.  Credit is extended to customers based on an evaluation of the customer’s financial condition and other factors.  Concentrations of credit risk with respect to trade receivables are monitored and this risk is reduced due to short-term payment terms relating to most of our significant customers.  Six customers (including their affiliates) account for approximately 36% of our total net receivables at December 31, 2017.