Pension Plan and Retirement Benefits - Defined Benefit Plans - Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Components of net periodic pension cost and postretirement health care benefit cost
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Nonoperating Retirement Benefit Expense	Nonoperating Retirement Benefit Expense	Nonoperating Retirement Benefit Expense
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Nonoperating Retirement Benefit Expense	Nonoperating Retirement Benefit Expense	Nonoperating Retirement Benefit Expense
Defined Benefit Pension Plan
Components of net periodic pension cost and postretirement health care benefit cost
Service cost	$ 4,728	$ 5,628	$ 5,546
Service cost	4,728	5,795
Interest cost	7,936	7,481	8,866
Expected return	(14,818)	(16,356)	(15,061)
Amortization of prior service cost	233	239	228
Recognized actuarial loss		7,721	7,288
Net periodic benefit cost	(1,921)	4,713	6,867
Defined Benefit Other Postretirement Benefit Plan
Components of net periodic pension cost and postretirement health care benefit cost
Service cost	1,825	1,095	1,416
Interest cost	2,234	2,292	3,493
Recognized actuarial loss	(240)		1,848
Net periodic benefit cost	$ 3,819	$ 3,387	$ 6,757