BUSINESS SEGMENT AND OTHER OPERATIONS DATA, RECONCILIATION OF SEGMENT INCOME TO CONSOLIDATED (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Utility										$ 594,346	$ 781,970	$ 819,415
Nonutility										1,286,559	1,952,017	2,918,730
Total operating revenues		$ 469,241	$ 393,213	$ 574,193	$ 444,258	$ 438,306	$ 458,467	$ 1,013,090	$ 824,124	1,880,905	2,733,987	3,738,145
Depreciation and amortization										72,748	61,399	52,742
Interest income	[1]									128	580	1,222
Interest expense, net of capitalized interest										31,044	27,721	25,463
Income tax provision (benefit)										23,530	59,724	51,840
Equity in earnings of affiliates										9,515	13,409	10,532
Net financial earnings										138,085	151,503	176,857
Capital expenditures										356,092	320,086	289,288
Investments in equity investees										$ 11,176	$ 5,780	$ 555
CANADA
Segment Reporting Information [Line Items]
Percentage to total operating revenues										2.00%	3.70%	3.30%
Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues										$ 1,845,139	$ 2,748,790	$ 3,764,807
Depreciation and amortization										71,893	60,478	51,900
Interest income	[1]									1,737	1,777	2,171
Interest expense, net of capitalized interest										31,616	28,095	25,104
Income tax provision (benefit)										21,519	58,468	49,122
Net financial earnings										135,837	148,290	174,091
Capital expenditures										354,196	319,877	288,109
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Depreciation and amortization										47,828	43,085	40,540
Interest income	[1]									115	336	999
Interest expense, net of capitalized interest										19,930	18,534	16,683
Income tax provision (benefit)										34,951	39,544	39,374
Net financial earnings										76,104	76,287	74,204
Capital expenditures										205,133	168,875	152,566
Operating Segments | Natural Gas Distribution | External customers
Segment Reporting Information [Line Items]
Utility										594,346	781,970	819,415
Operating Segments | Clean Energy Ventures
Segment Reporting Information [Line Items]
Depreciation and amortization										23,971	17,297	11,295
Interest income	[1]									0	26	0
Interest expense, net of capitalized interest										10,304	7,635	5,300
Income tax provision (benefit)										(26,592)	(26,968)	(21,937)
Net financial earnings										28,393	20,101	12,654
Capital expenditures										149,063	151,002	135,543
Operating Segments | Clean Energy Ventures | External customers
Segment Reporting Information [Line Items]
Nonutility										53,540	32,513	14,575
Operating Segments | Energy Services
Segment Reporting Information [Line Items]
Depreciation and amortization										88	90	59
Interest income	[1]									98	438	222
Interest expense, net of capitalized interest										1,095	1,209	1,725
Income tax provision (benefit)										7,030	39,043	26,458
Net financial earnings										21,934	42,122	79,735
Operating Segments | Energy Services | External customers
Segment Reporting Information [Line Items]
Nonutility	[2]									1,187,754	1,872,781	2,858,703
Operating Segments | Energy Services | Intercompany
Segment Reporting Information [Line Items]
Nonutility										9,499	61,526	72,114
Operating Segments | Midstream
Segment Reporting Information [Line Items]
Depreciation and amortization										6	6	6
Interest income	[1]									1,524	977	950
Interest expense, net of capitalized interest										287	717	1,396
Income tax provision (benefit)										6,130	6,849	5,227
Equity in earnings of affiliates										13,936	17,487	14,078
Net financial earnings										9,406	9,780	7,498
Investments in equity investees										11,176	5,780	555
Home Services and Other
Segment Reporting Information [Line Items]
Depreciation and amortization										981	952	846
Interest income	[1]									397	217	1
Interest expense, net of capitalized interest										252	49	359
Income tax provision (benefit)										1,387	1,551	2,460
Net financial earnings										2,882	3,420	2,798
Capital expenditures										1,896	209	1,179
Home Services and Other | External customers
Segment Reporting Information [Line Items]
Nonutility										45,265	46,723	45,452
Home Services and Other | Intercompany
Segment Reporting Information [Line Items]
Nonutility										3,232	1,980	1,235
Eliminations
Segment Reporting Information [Line Items]
Nonutility										(12,731)	(63,506)	(73,349)
Depreciation and amortization										(126)	(31)	(4)
Interest income	[1]									(2,006)	(1,414)	(950)
Interest expense, net of capitalized interest										(824)	(423)	0
Income tax provision (benefit)										624	(295)	258
Equity in earnings of affiliates										(4,421)	(4,078)	(3,546)
Net financial earnings										$ (634)	$ (207)	$ (32)

[1] Included in other income, net on the Consolidated Statements of Operations.

[2] Includes sales to Canada, which accounted for 2, 3.7 and 3.3 percent of total operating revenues during fiscal 2016, 2015 and 2014, respectively.