Annual report pursuant to Section 13 and 15(d)

Accounts receivable reserves

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Accounts receivable reserves
 12 Months Ended
Sep. 30, 2017
Receivables [Abstract]  
Accounts receivable reserves
Accounts receivable reserves
Changes in the reserves against accounts receivable were as follows (in thousands):
 
Year ended September 30,
 
2017
 
2016
 
2015
Balance at beginning of year
$
4,226

 
$
3,385

 
$
3,138

Additions to reserve
5,106

 
2,335

 
2,690

Deductions
(2,489
)
 
(1,494
)
 
(2,443
)
Balance at end of year
$
6,843

 
$
4,226

 
$
3,385


In evaluating the net realizable value of accounts receivable, we consider such factors as current economic trends, customer credit-worthiness, and changes in the customer payment terms and collection trends. Changes in the assumptions used in analyzing a specific account receivable may result in a reserve being recognized in the period in which the change occurs.
At September 30, 2017 and 2016, $10.3 million and $16.2 million of our unbilled receivables related to amounts pursuant to contractual retainage provisions. We anticipate that the majority of the fiscal 2017 balance will be collected during the 2018 fiscal year.