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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 1 (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Sep. 30, 2013
customer
Sep. 30, 2012
Sep. 30, 2011
Nature of operations [Abstract]      
Population of service area (more than) 1,130,000    
Utility Plant, Depreciation and Amortization [Abstract]      
Average annual depreciation and amortization expense percentage 3.20% 3.10% 3.10%
Annual capital expenditures $ 128.5 $ 106.7 $ 67.3
Accruals for capital expenditures $ 4.7 $ 9.7 $ 8.2