Fair value measurement - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, FV-NI, cost	$ 3,711	$ 3,711
Equity ownership, excluding consolidated entity and equity method investee, percentage	15.00%
Fair value, measurement with unobservable inputs reconciliation, recurring basis, liability value	$ 3,711	3,711
Prepaid Expenses and Other Current Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest receivable	1,200	$ 1,200
Convertible Note | Convertible Notes Payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities, FV-NI, cost	$ 3,500
Debt instrument, interest rate, stated percentage	4.00%