Other Income and Other Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other income:
Interest income	$ 2,699	$ 2,408	$ 5,001	$ 4,299
Miscellaneous	5	2	28	4
Total other income	12,885	6,598	20,054	10,583
Other expense:
Non-operating costs	(3,481)	(3,278)	(6,185)	(4,924)
Investment losses — net	(491)	(174)	(729)	(350)
Miscellaneous	(378)	(319)	(1,794)	(1,726)
Total other expense	(4,350)	(3,771)	(8,708)	(7,000)
APS
Other income:
Interest income	1,504	2,046	3,054	3,724
Miscellaneous	6	1	28	3
Total other income	11,691	6,235	18,107	10,007
Other expense:
Non-operating costs	(3,049)	(3,057)	(5,517)	(4,596)
Miscellaneous	(379)	(315)	(1,789)	(1,722)
Total other expense	(3,428)	(3,372)	(7,306)	(6,318)
SCR deferral
Other income:
Debt return on Four Corners SCR (Note 4)	4,887	4,188	9,731	6,280
SCR deferral | APS
Other income:
Debt return on Four Corners SCR (Note 4)	4,887	4,188	9,731	6,280
Ocotillo deferral
Other income:
Debt return on Four Corners SCR (Note 4)	5,294	0	5,294	0
Ocotillo deferral | APS
Other income:
Debt return on Four Corners SCR (Note 4)	$ 5,294	$ 0	$ 5,294	$ 0