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

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DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Mar. 13, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018	May 30, 2018	May 15, 2018	May 11, 2018	Jan. 31, 2018	Jun. 30, 2015
Fair Value
Derivative assets, current		$ 28,337		$ 28,337		$ 27,396
Derivative liabilities, current		40,677		40,677		46,652
Derivative assets, noncurrent		14,476		14,476		10,560
Derivative liabilities, noncurrent		24,923		24,923		22,982
Treasury lock
Derivatives, Fair Value [Line Items]
Benchmark interest rate											3.26%
Interest rate, stated percentage									4.01%
Gain (loss) on derivative, net	$ (2,600)
Interest rate swap
Derivatives, Fair Value [Line Items]
Benchmark interest rate										2.84%
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative, net		26,740	$ (2,752)	17,656	$ (93,209)
Fair Value
Derivative assets		42,813		42,813		37,956
Derivative liabilities		65,600		65,600		69,634
Natural Gas Distribution \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative, net		(9,556)	3,128	(1,904)	(5,836)
Natural Gas Distribution \| Not Designated as Hedging Instrument \| Physical commodity contracts
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative, net		812	(178)	5,225	(16,033)
Fair Value
Derivative assets, current		55		55		85
Derivative liabilities, current		62		62		192
Natural Gas Distribution \| Not Designated as Hedging Instrument \| Financial commodity contracts
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative, net		(10,368)	3,306	(7,129)	1,730
Fair Value
Derivative assets, current		216		216		94
Derivative liabilities, current		19		19		0
Natural Gas Distribution \| Not Designated as Hedging Instrument \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Gain (loss) on derivative, net		0	$ 0	0	$ 8,467
Natural Gas Distribution \| Series Ll
Derivatives, Fair Value [Line Items]
Debt issued								$ 125,000
Interest rate, stated percentage								5.60%
Energy Services \| Not Designated as Hedging Instrument \| Physical commodity contracts
Fair Value
Derivative assets, current		7,874		7,874		7,667
Derivative liabilities, current		17,988		17,988		18,158
Derivative assets, noncurrent		3,126		3,126		3,930
Derivative liabilities, noncurrent		19,068		19,068		11,316
Energy Services \| Not Designated as Hedging Instrument \| Financial commodity contracts
Fair Value
Derivative assets, current		20,162		20,162		19,169
Derivative liabilities, current		22,425		22,425		28,176
Derivative assets, noncurrent		11,350		11,350		6,630
Derivative liabilities, noncurrent		5,774		5,774		11,548
Energy Services \| Not Designated as Hedging Instrument \| Foreign currency contracts
Fair Value
Derivative assets, current		10		10		0
Derivative liabilities, current		183		183		126
Derivative assets, noncurrent		0		0		0
Derivative liabilities, noncurrent		81		81		118
First Mortgage \| Natural Gas Distribution \| Series VV
Derivatives, Fair Value [Line Items]
Debt issued							$ 125,000		$ 125,000
Term Loan \| Credit Agreement Due August 16, 2019 \| Interest rate swap
Derivatives, Fair Value [Line Items]
Debt issued										$ 100,000
Home Services and Other \| Not Designated as Hedging Instrument \| Interest rate contracts
Fair Value
Derivative assets, current		20		20		381
Derivative liabilities, current		$ 0		$ 0		$ 0