Financing receivable, net - Portfolio of risk rating (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Oct. 01, 2023	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022
Financing receivables, net:
Financing receivables, gross	$ 10,482			$ 12,254
Unearned interest income	(609)			(859)
Allowance for credit losses	(70)	$ (77)		0	$ 0	$ 0	$ 0
Financing receivables, net	9,803		$ 82	11,395
Short-term	7,625			7,171
Long-term	2,178			4,224
Low Risk Rating
Financing receivables, net:
Financing receivables, gross	7,235			8,893
Unearned interest income	(210)			(325)
Allowance for credit losses	(16)	(16)		0	0	0	0
Financing receivables, net	7,009			8,568
Short-term	6,701			6,281
Long-term	308			2,287
Moderate Risk Rating
Financing receivables, net:
Financing receivables, gross	3,247			3,361
Unearned interest income	(399)			(534)
Allowance for credit losses	(54)	$ (61)		0	$ 0	$ 0	$ 0
Financing receivables, net	2,794			2,827
Short-term	924			890
Long-term	$ 1,870			$ 1,937