Employee Retirement Plans (Reconciliations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
(Liabilities) recorded in the balance sheet:
Unfunded liabilities — included in other current liabilities	$ (17,885)	$ (15,802)
Unfunded liabilities — included in other noncurrent liabilities	(72,505)	(179,056)
Pension Benefits [Member]
Change in benefit obligations:
Benefit obligations - beginning of the year	543,605	456,714
Service cost	9,385	8,063
Interest cost	22,784	24,095
Actuarial loss (gain)	(69,112)	74,676
Plan amendments	993	0
Benefits paid	(21,187)	(19,943)
Benefit obligations - end of the year	486,468	543,605	456,714
Change in plan assets:
Fair value of plan assets - beginning of year	351,543	289,764
Actual gain on assets	45,450	50,550
Employer contributions	22,365	31,172	18,718
Benefits paid	(21,187)	(19,943)
Fair value of plan assets - end of year	398,171	351,543	289,764
Funded status of the plans - end of the year	(88,297)	(192,062)
(Liabilities) recorded in the balance sheet:
Assets in excess of liabilities — included in other noncurrent assets	0	0
Unfunded liabilities — included in other current liabilities	(17,885)	(15,802)
Unfunded liabilities — included in other noncurrent liabilities	(70,412)	(176,260)
Net amount recognized	(88,297)	(192,062)
Amounts recorded in stockholder’s equity (pre-tax):
Prior service cost (credit)	222	152
Net actuarial loss (gain)	9,113	18,099
Total	9,335	18,251
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost (credit)	2,223	1,550
Net actuarial loss	91,275	184,464
Total	93,498	186,014
Other Postretirement Benefits [Member]
Change in benefit obligations:
Benefit obligations - beginning of the year	14,560	13,333
Service cost	223	162
Interest cost	587	665
Actuarial loss (gain)	(1,881)	1,464
Plan amendments	(1,836)	0
Benefits paid	(965)	(1,064)
Benefit obligations - end of the year	10,688	14,560
Change in plan assets:
Fair value of plan assets - beginning of year	11,205	9,805
Actual gain on assets	1,117	1,741
Employer contributions	366	723
Benefits paid	(965)	(1,064)
Fair value of plan assets - end of year	11,723	11,205
Funded status of the plans - end of the year	1,035	(3,355)
(Liabilities) recorded in the balance sheet:
Assets in excess of liabilities — included in other noncurrent assets	3,252	0
Unfunded liabilities — included in other current liabilities	(372)	(654)
Unfunded liabilities — included in other noncurrent liabilities	(1,844)	(2,701)
Net amount recognized	1,036	(3,355)
Amounts recorded in stockholder’s equity (pre-tax):
Prior service cost (credit)	(74)	(79)
Net actuarial loss (gain)	(222)	164
Total	(296)	85
Amounts recorded in regulatory assets and liabilities (pre-tax):
Prior service cost (credit)	(4,286)	(2,766)
Net actuarial loss	3,586	5,815
Total	$ (700)	$ 3,049