CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
NET INCOME	$ 172,317	$ 126,182	$ 200,502	$ 135,508
Derivative instruments:
Net unrealized gain (loss), net of tax expense	7	128	(763)	(566)
Reclassification of net realized loss, net of tax expense	564	624	1,771	1,766
Pension and other postretirement benefits activity, net of tax expense	(1,334)	(701)	(812)	(171)
Total other comprehensive income (loss)	(763)	51	196	1,029
COMPREHENSIVE INCOME	171,554	126,233	200,698	136,537
Less: Comprehensive income attributable to noncontrolling interests	4,874	4,874	9,747	9,747
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	166,680	121,359	190,951	126,790
APS
NET INCOME	173,982	132,062	202,017	144,188
Derivative instruments:
Net unrealized gain (loss), net of tax expense	7	128	(763)	(566)
Reclassification of net realized loss, net of tax expense	564	624	1,771	1,766
Pension and other postretirement benefits activity, net of tax expense	(1,308)	(642)	(697)	(31)
Total other comprehensive income (loss)	(737)	110	311	1,169
COMPREHENSIVE INCOME	173,245	132,172	202,328	145,357
Less: Comprehensive income attributable to noncontrolling interests	4,874	4,874	9,747	9,747
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 168,371	$ 127,298	$ 192,581	$ 135,610