Employee Retirement Plans (Reconciliations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
(Liabilities) recorded in the balance sheet:
Unfunded liabilities - included in other current liabilities	$ (15,802)	$ (28,228)
Unfunded liabilities — included in other noncurrent liabilities	(179,056)	(142,248)
Pension Benefits [Member]
Change in benefit obligations:
Benefit obligations - beginning of the year	456,714	464,977
Service cost	8,063	8,151
Interest cost	24,095	23,815
Actuarial loss (gain)	74,676	(20,772)
Plan amendments	0	0
Benefits paid	(19,943)	(19,457)
Benefit obligations - end of the year	543,605	456,714	464,977
Change in plan assets:
Fair value of plan assets - beginning of year	289,764	287,902
Actual gain on assets	50,550	2,601
Employer contributions	31,172	18,718	3,353
Benefits paid	(19,943)	(19,457)
Fair value of plan assets - end of year	351,543	289,764	287,902
Funded status of the plans - end of the year	(192,062)	(166,950)
(Liabilities) recorded in the balance sheet:
Unfunded liabilities - included in other current liabilities	(15,802)	(27,600)
Unfunded liabilities — included in other noncurrent liabilities	(176,260)	(139,350)
Net amount recognized	(192,062)	(166,950)
Amounts recorded in stockholder’s equity (pre-tax):
Prior service cost (credit)	152	174
Net actuarial loss (gain)	18,099	14,452
Total	18,251	14,626
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost (credit)	1,550	1,775
Net actuarial loss	184,464	146,899
Total	186,014	148,674
Other Postretirement Benefits [Member]
Change in benefit obligations:
Benefit obligations - beginning of the year	13,333	15,140
Service cost	162	217
Interest cost	665	701
Actuarial loss (gain)	1,464	(1,516)
Plan amendments	0	(126)
Benefits paid	(1,064)	(1,083)
Benefit obligations - end of the year	14,560	13,333
Change in plan assets:
Fair value of plan assets - beginning of year	9,805	10,007
Actual gain on assets	1,741	149
Employer contributions	723	732
Benefits paid	(1,064)	(1,083)
Fair value of plan assets - end of year	11,205	9,805
Funded status of the plans - end of the year	(3,355)	(3,528)
(Liabilities) recorded in the balance sheet:
Unfunded liabilities - included in other current liabilities	(654)	(628)
Unfunded liabilities — included in other noncurrent liabilities	(2,701)	(2,898)
Net amount recognized	(3,355)	(3,526)
Amounts recorded in stockholder’s equity (pre-tax):
Prior service cost (credit)	(79)	(91)
Net actuarial loss (gain)	164	(168)
Total	85	(259)
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost (credit)	(2,766)	(3,188)
Net actuarial loss	5,815	6,294
Total	$ 3,049	$ 3,106