Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired					$ 1,050,000
Amortization of Intangible Assets	$ 51,763	$ 37,068	$ 103,784	$ 55,263
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			5 years
Maximum [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			20 years
Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			18 years
Trademarks [Member]
Goodwill And Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired					120,000
Customer Relationships [Member]
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired					920,800
Customer Relationships [Member] | Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			18 years 1 month 20 days
Beneficial Lease Arrangements [Member]
Goodwill And Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired					$ 7,000
Beneficial Lease Arrangements [Member] | Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			4 years 7 days