Employee and Retiree Benefit Plans (Components of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,254	$ 2,030	$ 4,509	$ 4,062
Interest cost	6,707	6,287			$ 13,444	$ 13,006
Expected return on plan assets	(7,453)	(6,475)			(14,959)	(13,660)
Amortization of prior service cost (credit)	256	254			513	508
Recognized actuarial loss	5,181	3,509			10,396	7,063
Net periodic benefit expense	6,945	5,605			13,903	10,979
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	493	424	$ 987	$ 849
Interest cost	874	967			1,748	1,933
Amortization of prior service cost (credit)	(9)	(19)			(19)	(37)
Net periodic benefit expense	$ 1,358	$ 1,372			$ 2,716	$ 2,745