Segment Information (Tables)

6 Months Ended

Mar. 31, 2017

Segment Reporting [Abstract]

Schedule of Segment Information

Financial information by business segment follows:

			Reportable Segments
Three Months Ended March 31, 2017	Total		Gas Utility		Electric Utility
Revenues	$	359,940	$	335,864	$	24,076
Cost of sales — gas, fuel and purchased power	$	164,541	$	150,863	$	13,678
Depreciation and amortization	$	17,699	$	16,378	$	1,321
Operating income	$	116,408	$	115,105	$	1,303
Interest expense	$	10,322	$	9,833	$	489
Income before income taxes	$	106,086	$	105,272	$	814
Capital expenditures (including the effects of accruals)	$	56,517	$	54,137	$	2,380

			Reportable Segments
Three Months Ended March 31, 2016	Total		Gas Utility		Electric Utility
Revenues	$	322,047	$	298,088	$	23,959
Cost of sales — gas, fuel and purchased power	$	137,434	$	123,702	$	13,732
Depreciation and amortization	$	17,030	$	15,822	$	1,208
Operating income	$	114,481	$	111,004	$	3,477
Interest expense	$	9,270	$	8,847	$	423
Income before income taxes	$	105,211	$	102,157	$	3,054
Capital expenditures (including the effects of accruals)	$	48,113	$	46,003	$	2,110

			Reportable Segments
Six Months Ended March 31, 2017	Total		Gas Utility		Electric Utility
Revenues	$	621,353	$	572,964	$	48,389
Cost of sales — gas, fuel and purchased power	$	274,012	$	246,430	$	27,582
Depreciation and amortization	$	35,090	$	32,533	$	2,557
Operating income	$	198,644	$	194,072	$	4,572
Interest expense	$	20,350	$	19,416	$	934
Income before income taxes	$	178,294	$	174,656	$	3,638
Capital expenditures (including the effects of accruals)	$	120,613	$	115,879	$	4,734
As of March 31, 2017
Total assets	$	2,909,725	$	2,746,144	$	163,581
Goodwill	$	182,145	$	182,145	$	—

			Reportable Segments
Six Months Ended March 31, 2016	Total		Gas Utility		Electric Utility
Revenues	$	520,029	$	475,030	$	44,999
Cost of sales — gas, fuel and purchased power	$	212,873	$	187,931	$	24,942
Depreciation and amortization	$	33,731	$	31,326	$	2,405
Operating income	$	162,777	$	156,824	$	5,953
Interest expense	$	18,764	$	17,913	$	851
Income before income taxes	$	144,013	$	138,911	$	5,102
Capital expenditures (including the effects of accruals)	$	109,577	$	105,273	$	4,304
As of March 31, 2016
Total assets	$	2,639,519	$	2,486,225	$	153,294
Goodwill	$	182,145	$	182,145	$	—