Guarantor And Non-Guarantor Subsidiaries Financial Information - Consolidating Statement of Cash Flows (Parenthetical) (Detail)	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
5.50% Senior Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate	5.50%	5.50%	5.50%
4.125% Senior Secured Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate		4.125%
6.00% Senior Secured Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate		6.00%
6.75% Senior Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate	6.75%
4.875% Senior Secured Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate		4.875%
6.25% Senior Secured Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate		6.25%
5.625% Senior Secured Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate		5.625%
5.00% Senior Secured Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate	5.00%	5.00%	5.00%
6.75% Senior Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate			6.75%
13.75% Senior Notes
Condensed Cash Flow Statements Captions [Line Items]
Interest rate	13.75%	13.75%	13.75%