Fair Value Measurements - Schedule of Carrying Values and Estimated Fair Values of Financial Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Sep. 30, 2025
Carrying Amount
Financial liabilities
Total financial liabilities	$ 1,030,996	$ 1,029,114
Carrying Amount | Senior Notes
Financial liabilities
Total financial liabilities	951,493	950,644
Carrying Amount | Junior Subordinated Notes
Financial liabilities
Total financial liabilities	79,503	78,470
Fair Value
Financial liabilities
Total financial liabilities	1,031,422	1,047,104
Fair Value | Senior Notes
Financial liabilities
Total financial liabilities	951,919	968,634
Fair Value | Junior Subordinated Notes
Financial liabilities
Total financial liabilities	$ 79,503	$ 78,470