Retirement and Post-Retirement Employee Benefit Plans Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 473,950	$ 450,932
Actual return on plan assets	63,524	52,596
Employer contributions	5,000	15,000
Benefits paid	(34,230)	(44,578)	[1]
Fair value of plan assets at end of year	508,244	473,950
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	0	0
Employer contributions	13,142	4,604
Benefits paid	(4,588)	(4,604)
Settlements	(8,554)	0
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	158,977	138,009
Actual return on plan assets	21,160	14,528
Employer contributions	13,687	16,592
Plan participants' contributions	4,936	4,289
Benefits paid	(13,970)	(14,441)
Fair value of plan assets at end of year	$ 184,790	$ 158,977

[1] Includes $12.8 million of one-time payments to eligible deferred vested participants who elected to receive a lump-sum payout of their pension benefits during fiscal 2016.