Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Apr. 30, 2019	Mar. 31, 2019
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	$ 1,268	$ 1,251	$ 1,233
Promissory note receivable due April 2024 | Estimated Fair Value
Financial assets:
Notes receivable, fair value	1,268	1,251	1,233
Promissory note receivable due April 2024 | Estimated Fair Value | Level 1
Financial assets:
Notes receivable, fair value	0	0	0
Promissory note receivable due April 2024 | Estimated Fair Value | Level 2
Financial assets:
Notes receivable, fair value	0	0	0
Promissory note receivable due April 2024 | Estimated Fair Value | Level 3
Financial assets:
Notes receivable, fair value	1,268	1,251	1,233
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	17,706	16,500	15,600
Promissory note receivable from Founders | Estimated Fair Value
Financial assets:
Notes receivable, fair value	17,706	16,500	15,600
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	17,706	16,500	15,600
Investments in unconsolidated affiliates | Carrying Value
Financial assets:
Investments in unconsolidated affiliates	13,162	10,987	10,681
Investments in unconsolidated affiliates | Estimated Fair Value
Financial assets:
Investments in unconsolidated affiliates	41,135	35,998	42,917
Investments in unconsolidated affiliates | Estimated Fair Value | Level 1
Financial assets:
Investments in unconsolidated affiliates	40,285	35,998	42,917
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	34,347	34,265	34,184
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	34,303	35,765	34,389
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	34,303	35,765	34,389
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	102,817	102,563	102,312
2025 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	97,171	96,137	94,690
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	97,171	96,137	94,690
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	223,756	223,284	222,791
2029 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	268,893	224,112	221,529
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	268,893	224,112	221,529
2029 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Debt instruments, fair value	$ 0	$ 0	$ 0