Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Sep. 30, 2019	Apr. 30, 2019
Promissory note receivable from Founders
Financial assets:
Notes receivable, fair value				$ 15,000
Promissory note receivable from Founders | Carrying Value
Financial assets:
Notes receivable, fair value	$ 16,317	$ 15,722	$ 17,073
Promissory note receivable from Founders | Estimated Fair Value
Financial assets:
Notes receivable, fair value	16,317	15,722	17,073
Promissory note receivable from Founders | Estimated Fair Value | Level 1
Financial assets:
Notes receivable, fair value	0	0	0
Promissory note receivable from Founders | Estimated Fair Value | Level 2
Financial assets:
Notes receivable, fair value	0	0	0
Promissory note receivable from Founders | Estimated Fair Value | Level 3
Financial assets:
Notes receivable, fair value	16,317	15,722	17,073
Investments in unconsolidated affiliates | Carrying Value
Financial assets:
Investments in unconsolidated affiliates	13,555	13,329	10,125
Investments in unconsolidated affiliates | Estimated Fair Value
Financial assets:
Investments in unconsolidated affiliates	43,328	42,496	39,528
Investments in unconsolidated affiliates | Estimated Fair Value | Level 1
Financial assets:
Investments in unconsolidated affiliates	42,478	41,646	39,528
Investments in unconsolidated affiliates | Estimated Fair Value | Level 2
Financial assets:
Investments in unconsolidated affiliates	0	0	0
Investments in unconsolidated affiliates | Estimated Fair Value | Level 3
Financial assets:
Investments in unconsolidated affiliates	850	850	0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Debt instruments, fair value			34,307
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value			34,733
2024 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Debt instruments, fair value			0
2024 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Debt instruments, fair value			34,733
2024 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Debt instruments, fair value			0
2025 Convertible Notes | Carrying Value
Financial liabilities:
Debt instruments, fair value	103,205	103,072	102,695
2025 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	102,339	100,401	94,173
2025 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Debt instruments, fair value	0	0	0
2025 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Debt instruments, fair value	102,339	100,401	94,173
2025 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Debt instruments, fair value	0	0	0
2029 Convertible Notes | Carrying Value
Financial liabilities:
Debt instruments, fair value	224,505	224,256	223,528
2029 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	289,887	273,700	236,900
2029 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Debt instruments, fair value	0	0	0
2029 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Debt instruments, fair value	289,887	273,700	236,900
2029 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Debt instruments, fair value	$ 0	$ 0	0
Promissory note receivable due April 2024
Financial assets:
Notes receivable, fair value					$ 1,100	$ 1,100
Promissory note receivable due April 2024 | Carrying Value
Financial assets:
Notes receivable, fair value			1,259
Promissory note receivable due April 2024 | Estimated Fair Value
Financial assets:
Notes receivable, fair value			1,259
Promissory note receivable due April 2024 | Estimated Fair Value | Level 1
Financial assets:
Notes receivable, fair value			0
Promissory note receivable due April 2024 | Estimated Fair Value | Level 2
Financial assets:
Notes receivable, fair value			0
Promissory note receivable due April 2024 | Estimated Fair Value | Level 3
Financial assets:
Notes receivable, fair value			$ 1,259