Relationship with Parent and Related Entities - Summary of Components of General Allocated Corporate Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Relationship With Parent And Related Entities Disclosure [Line Items]
Depreciation	$ 9,200	$ 6,200	$ 7,700
Amortization	$ 3,100	2,700	4,200
Parent
Relationship With Parent And Related Entities Disclosure [Line Items]
Facility		6,299	6,125
Depreciation		1,637	1,467
Amortization		22	1,150
Facility and other usage charges		7,958	8,742
Information services		8,633	7,947
Corporate and administrative services		22,166	18,414
Total		$ 38,757	$ 35,103