Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Apr. 30, 2019	Mar. 31, 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	$ 16,186	$ 16,500	$ 16,050
Promissory note receivable from Founders | Estimated Fair Value
Financial assets:
Notes receivable, fair value	16,186	16,500	16,050
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	16,186	16,500	16,050
Investments in unconsolidated affiliates | Carrying Value
Financial assets:
Investments in unconsolidated affiliates	12,297	10,987	10,247
Investments in unconsolidated affiliates | Estimated Fair Value
Financial assets:
Investments in unconsolidated affiliates	40,762	35,998	41,367
Investments in unconsolidated affiliates | Estimated Fair Value | Level 1
Financial assets:
Investments in unconsolidated affiliates	39,912	35,998	41,367
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	0	0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Debt instruments, fair value	34,386	34,265	34,223
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	34,690	35,765	36,126
2024 Convertible Notes | Estimated Fair Value | Level 1
Financial liabilities:
Debt instruments, fair value	0	0	0
2024 Convertible Notes | Estimated Fair Value | Level 2
Financial liabilities:
Debt instruments, fair value	34,690	35,765	36,126
2024 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Debt instruments, fair value	0	0	0
2025 Convertible Notes | Carrying Value
Financial liabilities:
Debt instruments, fair value	102,940	102,563	102,433
2025 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	99,238	96,137	94,586
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	99,238	96,137	94,586
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	223,998	223,284	223,030
2029 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	262,564	224,112	228,294
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	262,564	224,112	228,294
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		1,251	1,242
Promissory note receivable due April 2024 | Estimated Fair Value
Financial assets:
Notes receivable, fair value		1,251	1,242
Promissory note receivable due April 2024 | Estimated Fair Value | Level 1
Financial assets:
Notes receivable, fair value		0	0
Promissory note receivable due April 2024 | Estimated Fair Value | Level 2
Financial assets:
Notes receivable, fair value		0	0
Promissory note receivable due April 2024 | Estimated Fair Value | Level 3
Financial assets:
Notes receivable, fair value		$ 1,251	$ 1,242