Guarantor and Non-Guarantor Subsidiaries Financial Information - Additional Information (Detail)				6 Months Ended	12 Months Ended
	Nov. 05, 2018	Oct. 12, 2018	Oct. 09, 2018	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018
5.625% Senior Secured Notes due 2022
Condensed Financial Statements Captions [Line Items]
Interest rate				5.625%		5.625%
5.625% Senior Secured Notes due 2022 | Acquisition Corp.
Condensed Financial Statements Captions [Line Items]
Interest rate	5.625%			5.625%	5.625%
Due date of Senior Secured Notes	2022			2022	2022
5.00% Senior Secured Notes due 2023 | Acquisition Corp.
Condensed Financial Statements Captions [Line Items]
Interest rate				5.00%
Due date of Senior Secured Notes				2023
4.125% Senior Secured Notes due 2024 | Acquisition Corp.
Condensed Financial Statements Captions [Line Items]
Interest rate		4.125%	4.125%	4.125%	4.125%
Due date of Senior Secured Notes		2024		2024	2024
4.875% Senior Secured Notes due 2024
Condensed Financial Statements Captions [Line Items]
Interest rate				4.875%		4.875%
4.875% Senior Secured Notes due 2024 | Acquisition Corp.
Condensed Financial Statements Captions [Line Items]
Interest rate			4.875%	4.875%	4.875%
Due date of Senior Secured Notes			2024	2024	2024
5.50% Senior Notes due 2026 | Acquisition Corp.
Condensed Financial Statements Captions [Line Items]
Interest rate				5.50%
Due date of Senior Secured Notes				2026
3.625% Senior Secured Notes due 2026
Condensed Financial Statements Captions [Line Items]
Interest rate				3.625%
3.625% Senior Secured Notes due 2026 | Acquisition Corp.
Condensed Financial Statements Captions [Line Items]
Interest rate		3.625%	3.625%	3.625%
Due date of Senior Secured Notes			2026	2026