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Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2017
Accounting Policies [Abstract]  
Summary of Adjustments in Allowances for Doubtful Accounts and Sales Adjustments
The following table summarizes the changes in the allowances for doubtful accounts and sales adjustments:
 
Years Ended December 31,
 
2017
 
2016
 
2015
Balance at beginning of year
$
3,396

 
$
1,640

 
$
1,725

Provisions for losses - accounts receivable
4,110

 
4,484

 
1,756

Collection of accounts previously written off
—

 
—

 
153

Deductions for accounts charged off or credits issued
(2,079
)
 
(2,728
)
 
(1,994
)
Balance at end of year
$
5,427

 
$
3,396

 
$
1,640