Nuclear Decommissioning Trusts (Tables)

12 Months Ended

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

	Fair Value		Total  Unrealized  Gains		Total  Unrealized  Losses
December 31, 2016
Equity securities	$	353,261	$	188,091	$	—
Fixed income securities	425,530		9,820		(4,962		)
Net receivables (a)	795		—		—
Total	$	779,586	$	197,911	$	(4,962	)

	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.

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):

	Year Ended December 31,
	2016			2015			2014
Realized gains	$	11,213		$	5,189		$	4,725
Realized losses	(10,106		)	(6,225		)	(4,525		)
Proceeds from the sale of securities (a)	633,410			478,813			356,195

(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 December 31, 2016 is as follows (dollars in thousands):

	Fair Value
Less than one year	$	13,063
1 year – 5 years	119,292
5 years – 10 years	105,612
Greater than 10 years	187,563
Total	$	425,530