Accounts Receivable, Net
 12 Months Ended
Dec. 31, 2015
Text Block [Abstract]  
Accounts Receivable, Net
4.
Accounts Receivable, Net
 
As of December 31,
 
2015
 
2014
Accounts receivable, trade
$
154,497

 
$
280,657

Less allowance for doubtful accounts
(4,139
)
 
(3,976
)
Net accounts receivable, trade
150,358

 
276,681

Accounts receivable, other
10,490

 
12,743

Accounts receivable, net
$
160,848

 
$
289,424


Unbilled accounts receivable, included in accounts receivable, trade, at December 31, 2015 and 2014 were $47.8 million and $64.1 million, respectively. Unbilled receivables relate primarily to the delivery and sale of natural gas to customers in the current month for which the right to bill exists. Such amounts generally are invoiced to the customer the following month when actual usage data becomes available. Accounts receivable, other consists primarily of product tax receivables.

A reconciliation of the beginning and ending amount of allowance for doubtful accounts follows: 
 
Balance at
Beginning
of Period
 
Charged to
Expense
 
Charged (to)
from Another
Account
 
Deductions
 
Balance at
End of
Period
Balance, December 31, 2015:
 
 
 
 
 
 
 
 
 
Allowance for doubtful accounts
$
3,976

 
$
1,589

 
$
7

 
$
1,433

 
$
4,139

Allowance for notes receivable
2,367

 
—

 
(7
)
 
959

 
1,401

Total
$
6,343

 
$
1,589

 
$
—

 
$
2,392

 
$
5,540

Balance, December 31, 2014:
 
 
 
 
 
 
 
 
 
Allowance for doubtful accounts
$
1,607

 
$
2,350

 
$
84

 
$
65

 
$
3,976

Allowance for notes receivable
3,515

 
—

 
(84
)
 
1,064

 
2,367

Total
$
5,122

 
$
2,350

 
$
—

 
$
1,129

 
$
6,343

Balance, December 31, 2013:
 
 
 
 
 
 
 
 
 
Allowance for doubtful accounts
$
2,556

 
$
559

 
$
(740
)
 
$
768

 
$
1,607

Allowance for notes receivable
2,847

 
328

 
740

 
400

 
3,515

Total
$
5,403

 
$
887

 
$
—

 
$
1,168

 
$
5,122


Notes receivable, net of allowance, are generally long-term arrangements and are included in other assets, net and as of December 31, 2015 and 2014, were $0.5 million and $0.3 million, respectively.