Contractual interest rate for funds borrowed, under the debt agreement.

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DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) - USD ($) $ in Thousands		12 Months Ended
	Mar. 13, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	May 30, 2018	May 15, 2018	May 11, 2018	Jan. 26, 2018	Jun. 30, 2015
Derivatives, Fair Value [Line Items]
Asset Derivatives, current		$ 25,103	$ 27,396
Asset Derivatives, noncurrent		7,426	10,560
Liability Derivatives, current		57,623	46,652
Liability Derivatives, noncurrent		18,821	22,982
Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Amount of gain (loss) recognized in income on derivatives		(7,412)	(34,175)	$ 8,055
Asset Derivatives		32,529	37,956
Liability Derivatives		76,444	69,634
Treasury lock
Derivatives, Fair Value [Line Items]
Benchmark interest rate									3.26%
Interest rate, stated percentage							4.01%
Amount of gain (loss) recognized in income on derivatives	$ (2,600)
Term loan \| Credit Agreement Due August 16, 2019 \| Interest rate swap
Derivatives, Fair Value [Line Items]
Benchmark interest rate								2.84%
Debt issued								$ 100,000
Home Services and Other \| Interest rate contract \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current		0	381
Liability Derivatives, current		0	0
Natural Gas Distribution \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Amount of gain (loss) recognized in income on derivatives		(1,774)	11,543	7,898
Natural Gas Distribution \| Physical commodity contracts \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Amount of gain (loss) recognized in income on derivatives		5,926	1,232	(12,303)
Asset Derivatives, current		67	85
Liability Derivatives, current		245	192
Natural Gas Distribution \| Financial commodity contracts \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Amount of gain (loss) recognized in income on derivatives		(7,700)	1,844	5,595
Asset Derivatives, current		382	94
Liability Derivatives, current		570	0
Natural Gas Distribution \| Interest rate contract \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Amount of gain (loss) recognized in income on derivatives		0	8,467	$ 14,606
Natural Gas Distribution \| Series LL
Derivatives, Fair Value [Line Items]
Debt issued						$ 125,000
Interest rate, stated percentage						5.60%
Natural Gas Distribution \| First Mortgage \| Series VV
Derivatives, Fair Value [Line Items]
Debt issued					$ 125,000		$ 125,000
Energy Services \| Physical commodity contracts \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current		6,847	7,667
Asset Derivatives, noncurrent		1,710	3,930
Liability Derivatives, current		27,540	18,158
Liability Derivatives, noncurrent		12,641	11,316
Energy Services \| Financial commodity contracts \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current		17,806	19,169
Asset Derivatives, noncurrent		5,716	6,630
Liability Derivatives, current		29,057	28,176
Liability Derivatives, noncurrent		6,105	11,548
Energy Services \| Foreign currency contracts \| Derivatives not designated as hedging instruments:
Derivatives, Fair Value [Line Items]
Asset Derivatives, current		1	0
Asset Derivatives, noncurrent		0	0
Liability Derivatives, current		211	126
Liability Derivatives, noncurrent		$ 75	$ 118