Segment Information - Revenues and Long-Lived Assets by Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 192,444	$ 174,033	$ 184,939	$ 178,135	$ 166,839	$ 210,224	$ 223,280	$ 222,435	$ 729,551	$ 822,777	$ 847,229
Total long-lived tangible assets	53,811				56,986				53,811	56,986
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									553,581	638,844	650,413
Total long-lived tangible assets	30,651				36,361				30,651	36,361
Mexico
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									128,773	131,965	138,897
Total long-lived tangible assets	19,255				15,141				19,255	15,141
Other Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									46,777	48,146	52,288
Total long-lived tangible assets	$ 3,905				$ 5,484				3,905	5,484
Canada and other
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues									$ 420	$ 3,822	$ 5,631