Fair Value Measurements - Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 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	$ 1,259	$ 1,251	$ 1,224
Promissory note receivable due April 2024 | Estimated Fair Value
Financial assets:
Notes receivable, fair value	1,259	1,251	1,224
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	1,259	1,251	1,224
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	17,073	16,500	15,100
Promissory note receivable from Founders | Estimated Fair Value
Financial assets:
Notes receivable, fair value	17,073	16,500	15,100
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	17,073	16,500	15,100
Investments in unconsolidated affiliates | Carrying Value
Financial assets:
Investments in unconsolidated affiliates	10,125	10,987	37,789
Investments in unconsolidated affiliates | Estimated Fair Value
Financial assets:
Investments in unconsolidated affiliates	39,528	35,998	43,497
Investments in unconsolidated affiliates | Estimated Fair Value | Level 1
Financial assets:
Investments in unconsolidated affiliates	39,528	35,998	43,497
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	0	0	0
2024 Convertible Notes | Carrying Value
Financial liabilities:
Debt instruments, fair value	34,307	34,265	34,143
2024 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	34,733	35,765	35,851
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	34,733	35,765	35,851
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	102,695	102,563	102,192
2025 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	94,173	96,137	89,883
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	94,173	96,137	89,883
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	223,528	223,284	222,649
2029 Convertible Notes | Estimated Fair Value
Financial liabilities:
Debt instruments, fair value	236,900	224,112	225,975
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	236,900	224,112	225,975
2029 Convertible Notes | Estimated Fair Value | Level 3
Financial liabilities:
Debt instruments, fair value	$ 0	$ 0	$ 0