Goodwill and intangible assets - Summary of Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2023	Sep. 30, 2022
Goodwill [Roll Forward]
Balance at beginning of year	$ 85,811	$ 22,434
Business acquisition – additions	0	61,768
Remeasurement adjustments to the deferred tax assets	0	1,609
Balance at end of year	$ 85,811	$ 85,811