Retirement and Post-Retirement Employee Benefit Plans Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 434,767	$ 396,887
Actual return on plan assets	8,661	35,289
Employer contributions	38,000	27,110
Benefits paid	(30,496)	(24,519)
Fair value of plan assets at end of year	450,932	434,767
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	0	0
Employer contributions	4,551	21,902
Benefits paid	(4,551)	(5,085)
Settlements	0	(16,817)
Fair value of plan assets at end of year	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	134,821	106,413
Actual return on plan assets	(8,851)	14,003
Employer contributions	19,984	23,550
Plan participants' contributions	4,563	4,435
Benefits paid	(12,508)	(13,580)
Fair value of plan assets at end of year	$ 138,009	$ 134,821