DERIVATIVE INSTRUMENTS - BALANCE SHEET RELATED DISCLOSURES (Details) - USD ($)	Dec. 31, 2017	Sep. 30, 2017	Jun. 01, 2015
Derivatives, Fair Value [Line Items]
Benchmark interest rate			3.26%
Notional amount of foreign currency derivatives			$ 125,000,000
Fair Value
Derivative assets, current	$ 46,299,000	$ 30,081,000
Derivative liabilities, current	96,788,000	46,544,000
Derivative assets, noncurrent	5,537,000	9,164,000
Derivative liabilities, noncurrent	25,759,000	11,330,000
Derivative assets	51,836,000	39,245,000
Derivative liabilities	122,547,000	57,874,000
Foreign currency contracts
Derivatives, Fair Value [Line Items]
Notional amount of foreign currency derivatives	9,700,000
Energy Services | Not Designated as Hedging Instrument | Physical commodity contracts
Fair Value
Derivative assets, current	13,247,000	14,588,000
Derivative liabilities, current	24,531,000	16,589,000
Derivative assets, noncurrent	2,801,000	7,127,000
Derivative liabilities, noncurrent	14,256,000	8,710,000
Energy Services | Not Designated as Hedging Instrument | Financial commodity contracts
Fair Value
Derivative assets, current	32,559,000	15,302,000
Derivative liabilities, current	56,188,000	20,267,000
Derivative assets, noncurrent	2,706,000	2,033,000
Derivative liabilities, noncurrent	11,477,000	2,620,000
Energy Services | Not Designated as Hedging Instrument | Foreign currency contracts
Fair Value
Derivative assets, current	6,000	40,000
Derivative liabilities, current	4,000	0
Derivative assets, noncurrent	30,000	4,000
Derivative liabilities, noncurrent	26,000	0
Natural Gas Distribution | Not Designated as Hedging Instrument | Physical commodity contracts
Fair Value
Derivative assets, current	487,000	151,000
Derivative liabilities, current	53,000	72,000
Natural Gas Distribution | Not Designated as Hedging Instrument | Financial commodity contracts
Fair Value
Derivative assets, current	0	0
Derivative liabilities, current	3,478,000	1,149,000
Natural Gas Distribution | Not Designated as Hedging Instrument | Interest rate contracts
Fair Value
Derivative assets, current	0	0
Derivative liabilities, current	12,534,000	$ 8,467,000
Natural Gas Distribution | Series Ll
Derivatives, Fair Value [Line Items]
Debt issued	$ 125,000,000
Interest rate, stated percentage	5.60%