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Nuclear Decommissioning Trusts
 9 Months Ended
Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]  
Nuclear Decommissioning Trusts
Nuclear Decommissioning Trusts
 
To fund the costs APS expects to incur to decommission Palo Verde, APS established external decommissioning trusts in accordance with NRC regulations.  Third-party investment managers are authorized to buy and sell securities per stated investment guidelines.  The trust funds are invested in fixed income securities and equity securities.  APS classifies investments in decommissioning trust funds as available for sale.  As a result, we record the decommissioning trust funds at their fair value on our Condensed Consolidated Balance Sheets.  See Note 10 for a discussion of how fair value is determined and the classification of the nuclear decommissioning trust investments within the fair value hierarchy.  Because of the ability of APS to recover decommissioning costs in rates and in accordance with the regulatory treatment for decommissioning trust funds, we have deferred realized and unrealized gains and losses (including other-than-temporary impairments on investment securities) in other regulatory liabilities.  The following table includes the unrealized gains and losses based on the original cost of the investment and summarizes the fair value of APS’s nuclear decommissioning trust fund assets at September 30, 2016 and December 31, 2015 (dollars in thousands):
 
 
Fair Value
 
Total
Unrealized
Gains
 
Total
Unrealized
Losses
September 30, 2016
 

 
 

 
 

Equity securities
$
340,436

 
$
176,495

 
$
(3
)
Fixed income securities
434,285

 
20,804

 
(465
)
Net receivables (a)
5,032

 
—

 
—

Total
$
779,753

 
$
197,299

 
$
(468
)

 
Fair Value
 
Total
Unrealized
Gains
 
Total
Unrealized
Losses
December 31, 2015
 

 
 

 
 

Equity securities
$
314,957

 
$
157,098

 
$
(115
)
Fixed income securities
420,574

 
11,955

 
(2,645
)
Net payables (a)
(335
)
 
—

 
—

Total
$
735,196

 
$
169,053

 
$
(2,760
)
(a)
Net receivables/payables relate to pending purchases and sales of securities.

The costs of securities sold are determined on the basis of specific identification.  The following table sets forth approximate gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds (dollars in thousands):
 
Three Months Ended 
 September 30,
 
Nine Months Ended 
 September 30,
 
2016
 
2015
 
2016
 
2015
Realized gains
$
4,033

 
$
1,919

 
$
8,753

 
$
4,374

Realized losses
(3,345
)
 
(2,106
)
 
(6,481
)
 
(4,156
)
Proceeds from the sale of securities (a)
156,825

 
104,525

 
447,419

 
330,304

(a)
Proceeds are reinvested in the trust.
 
The fair value of fixed income securities, summarized by contractual maturities, at September 30, 2016 is as follows (dollars in thousands):
 
Fair Value
Less than one year
$
8,429

1 year – 5 years
134,200

5 years – 10 years
102,835

Greater than 10 years
188,821

Total
$
434,285