Income Taxes - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2019 USD ($) State Province	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Operating loss carryforwards	$ 31,500,000			$ 135,300,000
Net operating loss carryforward utilized	26,300,000
Goodwill	2,490,590,000	$ 2,491,779,000	$ 1,251,986,000
Goodwill amortizable for income tax	1,100,000,000
Uncertain tax positions	$ 0
U.S. [Member]
Number of States in which Entity Operates | State	50
Canada [Member]
Number of provinces in which entity operates | Province	6