Pension Plan and Retirement Benefits - Defined Benefit Plans - Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Change in Benefit Obligation:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Nonoperating Retirement Benefit Expense	Nonoperating Retirement Benefit Expense
Defined Benefit Pension Plan
Change in Benefit Obligation:
Projected benefit obligation at beginning of year	$ 315,466	$ 345,390
Service cost	4,728	5,795
Interest cost	7,936	7,481	$ 8,866
Actuarial gains (losses)	(81,225)	(27,225)
Benefits paid	(15,223)	(14,965)
Administrative expenses	(407)	(1,010)
Projected benefit obligation at end of year	231,275	315,466	345,390
Change in Plan Assets:
Fair value of plan assets at beginning of year	297,703	245,546
Actual return on assets	(69,752)	47,132
Contribution to plan	6,000	21,000
Benefits paid	(15,223)	(14,965)
Administrative expenses	(407)	(1,010)
Fair value of plan assets at end of year	218,321	297,703	245,546
Funded Status of Plan:
Unfunded status	(12,954)	(17,763)
Defined Benefit Other Postretirement Benefit Plan
Change in Benefit Obligation:
Projected benefit obligation at beginning of year	82,964	93,339
Service cost	1,825	1,095	1,416
Interest cost	2,234	2,292	3,493
Actuarial gains (losses)	(20,343)	(10,943)
Benefits paid	(2,643)	(2,819)
Projected benefit obligation at end of year	64,037	82,964	$ 93,339
Change in Plan Assets:
Contribution to plan	2,643	2,819
Benefits paid	(2,643)	(2,819)
Funded Status of Plan:
Unfunded status	$ (64,037)	$ (82,964)