Other Financial Information - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Nov. 18, 2025	Sep. 30, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Other Financials Information [Line Items]
Accrued contract costs including professional liability accruals		$ 1,419,000	$ 1,419,000	$ 1,354,700
Restructuring expenses incurred			59,355	98,918	$ 188,404
Accrued restructuring expenses		$ 15,000	15,000	11,900
Cash dividends declared (in dollars per share)		$ 0.26
Accrued and unpaid dividend		$ 37,600	37,600
Subsequent Event
Other Financials Information [Line Items]
Cash dividends declared (in dollars per share)	$ 0.31
Labor-Related Costs
Other Financials Information [Line Items]
Restructuring expenses incurred			32,000	18,700
Non-Labor Costs
Other Financials Information [Line Items]
Restructuring expenses incurred			27,300	80,200
Professional Liability Accrual
Other Financials Information [Line Items]
Accrued contract costs including professional liability accruals		$ 893,700	$ 893,700	$ 831,800