Nuclear Decommissioning Trusts (Tables)

3 Months Ended

Mar. 31, 2016

Investments, Debt and Equity Securities [Abstract]

Fair value of APS's nuclear decommissioning trust fund assets

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 March 31, 2016 and December 31, 2015 (dollars in thousands):

	Fair Value			Total Unrealized Gains		Total Unrealized Losses
March 31, 2016
Equity securities	$	319,971		$	159,790	$	(65	)
Fixed income securities	433,881			18,250		(676		)
Net payables (a)	(1,898		)	—		—
Total	$	751,954		$	178,040	$	(741	)

	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 payables relate to pending purchases and sales of securities.

Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds

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   March 31,
	2016			2015
Realized gains	$	2,438		$	1,195
Realized losses	(1,786		)	(525		)
Proceeds from the sale of securities (a)	141,809			115,282

(a) Proceeds are reinvested in the trust.

Fair value of fixed income securities, summarized by contractual maturities

The fair value of fixed income securities, summarized by contractual maturities, at March 31, 2016 is as follows (dollars in thousands):

	Fair Value
Less than one year	$	11,633
1 year – 5 years	126,221
5 years – 10 years	101,773
Greater than 10 years	194,254
Total	$	433,881