Summary of Significant Accounting Policies - Summary of valuation techniques and observable inputs can vary by investment (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 7,859	$ 43,940
ZEN receivable, related party		1,139
Investment in Horizen
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	7,859	42,801	$ 2,502
Level 1
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
ZEN receivable, related party		0
Level 1 | Investment in Horizen
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	0	0
Level 2
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
ZEN receivable, related party		1,139
Level 2 | Investment in Horizen
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	7,859	42,801
Level 3
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
ZEN receivable, related party		0
Level 3 | Investment in Horizen
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in ZEN	$ 0	$ 0