Other Income and Other Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other income:
Interest income	$ 2,302	$ 1,891
Debt return on Four Corners SCR (Note 4)	4,844	2,092
Miscellaneous	23	2
Total other income	7,169	3,985
Other expense:
Non-operating costs	(2,704)	(1,646)
Investment losses — net	(238)	(176)
Miscellaneous	(1,416)	(1,407)
Total other expense	(4,358)	(3,229)
APS
Other income:
Interest income	1,550	1,678
Debt return on Four Corners SCR (Note 4)	4,844	2,092
Miscellaneous	22	2
Total other income	6,416	3,772
Other expense:
Non-operating costs	(2,467)	(1,539)
Miscellaneous	(1,411)	(1,406)
Total other expense	$ (3,878)	$ (2,945)