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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 3 (Details) (USD $)
 12 Months Ended 12 Months Ended 165 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Unamortized investment tax credits [Member]
Sep. 30, 2012
Unamortized investment tax credits [Member]
Sep. 30, 2013
Accrued cost of removal [Member]
Sep. 30, 2012
Accrued cost of removal [Member]
Sep. 30, 2013
Other Regulatory Liabilities [Member]
Sep. 30, 2012
Other Regulatory Liabilities [Member]
Sep. 30, 2013
Future income taxes due from customers [Member]
Sep. 30, 2012
Future income taxes due from customers [Member]
Sep. 30, 2013
Pension and postretirement benefit costs [Member]
Sep. 30, 2012
Pension and postretirement benefit costs [Member]
Sep. 30, 2013
Unamortized purchased gas adjustments [Member]
Sep. 30, 2012
Unamortized purchased gas adjustments [Member]
Sep. 30, 2013
Purchased gas costs [Member]
Sep. 30, 2012
Purchased gas costs [Member]
Sep. 30, 2013
Compensated absences [Member]
Sep. 30, 2012
Compensated absences [Member]
Sep. 30, 2013
Other [Member]
Sep. 30, 2012
Other [Member]
Sep. 30, 2013
Deferred Costs Incurred Prior to YE 1999 [Member]
Sep. 30, 2013
Deferred Costs Incurred Prior to YE 1999 [Member]
Sep. 01, 2013
Missouri Gas Energy (MGE) [Member]
Sep. 01, 2013
Laclede Group [Member]
Missouri Gas Energy (MGE) [Member]
Schedule of Regulatory Assets and Liabilities[Line Items]                                                
Regulatory Assets $ 563,480,000 $ 496,721,000             $ 112,912,000 $ 118,997,000 $ 381,395,000 $ 304,446,000 $ 17,533,000 $ 40,674,000 $ 18,249,000 $ 18,386,000 $ 8,004,000 $ 7,836,000 $ 25,387,000 $ 6,382,000        
Regulatory Liabilities 85,460,000 59,432,000 2,900,000 3,113,000 59,066,000 55,103,000 23,494,000 1,216,000                                
Regulated Operations [Abstract]                                                
Regulatory assets not earning a rate of return 17,200,000 7,800,000                                            
Regulatory assets not earning a rate of return, recovery period 15 years                                              
Regulatory Assets - Non-current 545,947,000 456,047,000                                     10,500,000 10,500,000    
Amortization period of deferred costs (in years)                                         15 years      
Amortization of deferred costs recognized to date - total                                           9,700,000    
The amount by which the replacement cost exceeds (less than) the cost basis value of stored gas inventories 13,300,000 24,300,000                                            
Goodwill [Abstract]                                                
Goodwill acquired during period 247,078,000 0                                         247,078,000 247,100,000
Revenue Recognition [Abstract]                                                
Accrued Unbilled Revenue $ 25,200,000 $ 11,600,000