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Investments | 12 Months Ended
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Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |
Investments | Investments We have investments in debt and equity securities held in Nuclear Decommissioning Trusts and Coal Reclamation Escrow Accounts. These investments are classified as available for sale securities, and as a result we record the investments at their fair value on our Consolidated Balance Sheets. See Note 13 for a discussion of how fair value is determined and the classification of the investments within the fair value hierarchy. Because of the ability of APS to recover decommissioning and coal reclamation costs in rates, and in accordance with the regulatory treatment, APS has deferred realized and unrealized gains and losses (including other-than-temporary impairments on investment securities) in other regulatory liabilities. The costs of securities sold are determined on the basis of specific identification. 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. 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 December 31, 2017 and December 31, 2016 (dollars in thousands):
| December 31, 2017 |  | December 31, 2016
| Fair Value |  | Total Unrealized Gains |  | Total Unrealized Losses |  | Fair Value |  | Total Unrealized Gains |  | Total Unrealized Losses
Equity securities | $ | 417,390 |  |  | $ | 248,623 |  |  | $ | — |  |  | $ | 353,261 |  |  | $ | 188,091 |  |  | $ | — |
Fixed income securities | 446,277 |  |  | 11,537 |  |  | (2,996 | ) |  | 425,530 |  |  | 9,820 |  |  | (4,962 | )
Cash and cash equivalents | 7,224 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Net receivables (a) | 109 |  |  | — |  |  | — |  |  | 795 |  |  | — |  |  | — |
Total | $ | 871,000 |  |  | $ | 260,160 |  |  | $ | (2,996 | ) |  | $ | 779,586 |  |  | $ | 197,911 |  |  | $ | (4,962 | )
(a) | Net receivables/(payables) relate to pending purchases and sales of securities.
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):
| Nuclear Decommissioning
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
Realized gains | $ | 21,813 |  |  | $ | 11,213 |  |  | $ | 5,189 |
Realized losses | (13,146 | ) |  | (10,106 | ) |  | (6,225 | )
Proceeds from the sale of securities (a) | 542,246 |  |  | 633,410 |  |  | 478,813 |
(a) | Proceeds are reinvested in the trust/account.
Coal Reclamation Escrow Accounts APS has investments restricted for coal mine reclamation funding related to Four Corners. As of December 31, 2017, APS’s coal reclamation escrow accounts are invested in fixed income securities with a fair value of $30 million. The realized and unrealized gains and losses relating to these fixed income securities was immaterial for the twelve months ended December 31, 2017 and December 31, 2016. The proceeds from the sale of securities for the twelve months ended December 31, 2017 was $4 million. There were no proceeds from the sale of securities for the twelve months ended December 31, 2016. The proceeds are reinvested in the escrow accounts. 4CA also has investments restricted for coal mine reclamation funding relating to Four Corners invested in fixed income securities. The 4CA fixed income investments have a fair value of $2 million as of December 31, 2017. The realized and unrealized gains and losses relating to these fixed income securities was immaterial for the twelve months ended December 31, 2017 and 2016. Fixed Income Securities Contractual Maturities The fair value of fixed income securities, summarized by contractual maturities, at December 31, 2017 is as follows (dollars in thousands):
| Nuclear Decommissioning Trusts |  | Escrow Accounts |  | Total
Less than one year | $ | 24,668 |  |  | $ | 455 |  |  | $ | 25,123 |
1 year – 5 years | 100,289 |  |  | 2,494 |  |  | 102,783 |
5 years – 10 years | 129,239 |  |  | 8,615 |  |  | 137,854 |
Greater than 10 years | 192,081 |  |  | 20,453 |  |  | 212,534 |
Total | $ | 446,277 |  |  | $ | 32,017 |  |  | $ | 478,294 |

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- Definition The entire disclosure for investments in certain debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=4738149 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2176304 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2324412 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2209399 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 954 -SubTopic 320 -URI http://asc.fasb.org/subtopic&trid=2289146 + Details
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