Accounts Receivable, Net
 12 Months Ended
Dec. 31, 2016
Receivables [Abstract]  
Accounts Receivable, Net
4.
Accounts Receivable, Net
 
As of December 31,
 
2016
 
2015
Accounts receivable, trade
$
217,731

 
$
154,497

Less allowance for doubtful accounts
(4,282
)
 
(4,139
)
Net accounts receivable, trade
213,449

 
150,358

Accounts receivable, other
8,505

 
10,490

Accounts receivable, net
$
221,954

 
$
160,848


Unbilled accounts receivable, included in accounts receivable, trade, at December 31, 2016 and 2015 were $50.9 million and $47.8 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, 2016:
 
 
 
 
 
 
 
 
 
Allowance for doubtful accounts
$
4,139

 
$
230

 
$
20

 
$
(107
)
 
$
4,282

Allowance for notes receivable
1,401

 
—

 
(20
)
 
(740
)
 
641

Total
$
5,540

 
$
230

 
$
—

 
$
(847
)
 
$
4,923

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


Notes receivable, net of allowance, are generally long-term arrangements and are included in other assets, net and as of December 31, 2016, was less than $0.1 million and as of December 31, 2015, was $0.5 million.