Fair Value Measurements - Schedule of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Sep. 30, 2025	Mar. 31, 2025
Carrying Value
Financial assets:
Promissory note receivable from Founders		$ 24,369	$ 16,921
Investments in unconsolidated affiliates	$ 26,093	18,123	13,967
Carrying Value | 2025 Convertible Notes
Financial liabilities:
Debt instruments, fair value			103,325
Carrying Value | 2029 Convertible Notes
Financial liabilities:
Debt instruments, fair value	225,751	225,258	224,723
Carrying Value | 2032 Senior Notes
Financial liabilities:
Debt instruments, fair value	293,250	292,818	292,465
Estimated Fair Value
Financial assets:
Promissory note receivable from Founders		24,369	16,921
Investments in unconsolidated affiliates	61,839	59,729	42,199
Estimated Fair Value | 2025 Convertible Notes
Financial liabilities:
Debt instruments, fair value			104,024
Estimated Fair Value | 2029 Convertible Notes
Financial liabilities:
Debt instruments, fair value	558,257	422,931	338,089
Estimated Fair Value | 2032 Senior Notes
Financial liabilities:
Debt instruments, fair value	313,420	320,734	305,117
Estimated Fair Value | Level 1
Financial assets:
Promissory note receivable from Founders		0	0
Investments in unconsolidated affiliates	60,459	58,573	41,349
Estimated Fair Value | Level 1 | 2025 Convertible Notes
Financial liabilities:
Debt instruments, fair value			0
Estimated Fair Value | Level 1 | 2029 Convertible Notes
Financial liabilities:
Debt instruments, fair value	0	0	0
Estimated Fair Value | Level 1 | 2032 Senior Notes
Financial liabilities:
Debt instruments, fair value	0	0	0
Estimated Fair Value | Level 2
Financial assets:
Promissory note receivable from Founders		0	0
Investments in unconsolidated affiliates	0	0	0
Estimated Fair Value | Level 2 | 2025 Convertible Notes
Financial liabilities:
Debt instruments, fair value			104,024
Estimated Fair Value | Level 2 | 2029 Convertible Notes
Financial liabilities:
Debt instruments, fair value	558,257	422,931	338,089
Estimated Fair Value | Level 2 | 2032 Senior Notes
Financial liabilities:
Debt instruments, fair value	313,420	320,734	305,117
Estimated Fair Value | Level 3
Financial assets:
Promissory note receivable from Founders		24,369	16,921
Investments in unconsolidated affiliates	1,380	1,156	850
Estimated Fair Value | Level 3 | 2025 Convertible Notes
Financial liabilities:
Debt instruments, fair value			0
Estimated Fair Value | Level 3 | 2029 Convertible Notes
Financial liabilities:
Debt instruments, fair value	0	0	0
Estimated Fair Value | Level 3 | 2032 Senior Notes
Financial liabilities:
Debt instruments, fair value	$ 0	$ 0	$ 0