SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES , RELATED RISKS AND UNCERTAINTIES - Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Restricted Cash and Investments
Cash and cash equivalents	$ 214,104	$ 257,174	$ 229,186	$ 232,131
Restricted cash and cash equivalents	65,100	59,100	42,500	36,900
Total cash, cash equivalents, and restricted cash	279,241	316,238	271,658	269,009
Restricted cash
Restricted Cash and Investments
Restricted cash and cash equivalents	65,137	59,064	42,472	36,246
Other assets, net
Restricted Cash and Investments
Restricted cash and cash equivalents	$ 0	$ 0	$ 0	$ 632