Interim Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Components of net periodic pension cost [Abstract]
Service Cost	$ 4,560	$ 5,216
Interest Cost	6,430	6,297
Expected return on assets	(6,917)	(6,994)
Amortization of prior service (credit)/cost	(58)	(58)
Amortization of actuarial (gain) loss	3,089	4,249
Net periodic pension cost	$ 7,104	$ 8,710
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost Abstract
Discount Rate	3.89%	3.73%
Rate of compensation increase	3.50%	3.50%
Expected return on plan assets	6.75%	7.00%
Other Benefits [Member]
Components of net periodic pension cost [Abstract]
Service Cost	$ 3,020	$ 3,109
Interest Cost	2,727	2,670
Expected return on assets	(2,002)	(1,796)
Amortization of prior service (credit)/cost	3	(411)
Amortization of actuarial (gain) loss	(1,618)	(707)
Net periodic pension cost	$ 2,130	$ 2,865
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost Abstract
Discount Rate	3.89%	3.73%
Expected return on plan assets	4.29%	4.45%
Current Year Benefit Plan Contributions [Abstract]
Contributions Actual	$ 3,900
Other Benefits [Member] | Minimum [Member]
Current Year Benefit Plan Contributions [Abstract]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	10,000
Other Benefits [Member] | Maximum [Member]
Current Year Benefit Plan Contributions [Abstract]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 20,000