Retirement and Post-Retirement Employee Benefit Plans Net Periodic Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18,109	$ 16,419	$ 16,231
Interest cost	20,443	23,193	21,850
Expected return on assets	(27,975)	(27,522)	(25,744)
Amortization of prior service cost	(231)	(226)	(192)
Recognized actuarial loss	12,744	10,693	13,322
Net periodic pension cost	23,090	22,557	25,467
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,756	2,371	3,971
Interest cost	4,744	5,185	4,943
Amortization of transition asset	0	0	0
Amortization of prior service cost	0	0	0
Recognized actuarial loss	4,251	2,586	2,343
Settlements	2,685	0	0
Net periodic pension cost	14,436	10,142	11,257
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	12,436	10,823	15,583
Interest cost	10,679	12,424	14,385
Expected return on assets	(7,185)	(6,264)	(6,431)
Amortization of transition asset	0	82	272
Amortization of prior service cost	(1,644)	(1,644)	(1,644)
Recognized actuarial loss	(2,827)	(2,167)	0
Net periodic pension cost	$ 11,459	$ 13,254	$ 22,165