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Accounts Receivable
12 Months Ended
Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]  
Accounts Receivable Accounts Receivable

Net accounts receivable consisted of the following as of December 31, 2019 and 2018 (in thousands):
 
 
December 31, 2019
 
December 31, 2018
Trade accounts receivable
$
396,204

 
$
337,445

Unbilled accounts receivable
157,619

 
143,978

Gross accounts receivable
553,823

 
481,423

Allowance for doubtful accounts and other reserves
(1,880
)
 
(1,534
)
Accounts receivable, net
$
551,943

 
$
479,889



A summary of activity in the accounts receivable reserves for the years ended December 31, 2019, 2018 and 2017 is as follows (in thousands):

 
2019
 
2018
 
2017
Beginning balance
$
1,534

 
$
1,281

 
$
925

Charges to income from operations
5,116

 
3,824

 
3,407

Collections from customers previously reserved and other
(4,770
)
 
(3,571
)
 
(3,051
)
Ending balance
$
1,880

 
$
1,534

 
$
1,281



Charges to income from operations primarily represents charges to bad debt expense for increases in the allowance for doubtful accounts.