Summary of Significant Accounting Policies - Summary of Fair Value Estimates (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023	Sep. 30, 2022
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 8,804	$ 4,671	$ 8,691
Investment, Type [Extensible Enumeration]	Investment in ZEN	Investment in ZEN
Investment in ZEN
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 8,804	$ 4,671
Level 1
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 8,804	$ 4,671
Investment, Type [Extensible Enumeration]	Investment in ZEN	Investment in ZEN
Level 2
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 0	$ 0
Investment, Type [Extensible Enumeration]	Investment in ZEN	Investment in ZEN
Level 3
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 0	$ 0
Investment, Type [Extensible Enumeration]	Investment in ZEN	Investment in ZEN