Segment Information - Revenues and Long-Lived Assets by Geographic Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 1,049,041	$ 886,225	$ 729,551
Property and equipment, net	68,096	56,725
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	761,921	658,762	553,581
Property and equipment, net	37,695	32,594
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	223,765	173,122	128,773
Property and equipment, net	24,033	19,805
Other Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	63,300	54,230	46,777
Property and equipment, net	6,368	4,326
Canada and other
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 55	$ 111	$ 420