Segment Information (Tables)

3 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Schedule of Segment Information

Financial information by business segment follows:

			Reportable Segments
Three Months Ended December 31, 2017	Total		Gas Utility		Electric Utility
Revenues	$	323,105	$	299,965	$	23,140
Cost of sales — gas, fuel and purchased power	$	151,774	$	138,858	$	12,916
Depreciation and amortization	$	20,354	$	19,000	$	1,354
Operating income	$	96,295	$	93,681	$	2,614
Interest expense	$	10,939	$	10,526	$	413
Income before income taxes	$	85,356	$	83,155	$	2,201
Capital expenditures (including the effects of accruals)	$	71,699	$	68,842	$	2,857
As of December 31, 2017
Total assets	$	3,174,693	$	3,038,250	$	136,443
Goodwill	$	182,145	$	182,145	$	—

			Reportable Segments
Three Months Ended December 31, 2016	Total		Gas Utility		Electric Utility
Revenues	$	261,413	$	237,100	$	24,313
Cost of sales — gas, fuel and purchased power	$	109,471	$	95,567	$	13,904
Depreciation and amortization	$	17,391	$	16,155	$	1,236
Operating income	$	82,236	$	78,967	$	3,269
Interest expense	$	10,028	$	9,583	$	445
Income before income taxes	$	72,208	$	69,384	$	2,824
Capital expenditures (including the effects of accruals)	$	64,096	$	61,742	$	2,354
As of December 31, 2016
Total assets	$	2,898,523	$	2,736,908	$	161,615
Goodwill	$	182,145	$	182,145	$	—