Indebtedness - Debt Outstanding (Parenthetical) (Detail)	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
4.875% Senior Notes Due 2025
Debt Instrument [Line Items]
Interest rate on notes	4.875%		4.875%
5.00% Senior Notes Due 2022
Debt Instrument [Line Items]
Interest rate on notes	5.00%	5.00%	5.00%	5.00%
5.00% Senior Notes Due 2023
Debt Instrument [Line Items]
Interest rate on notes	5.00%	5.00%	5.00%
5.75% Senior Notes Due 2021
Debt Instrument [Line Items]
Interest rate on notes	5.75%	5.75%	5.75%	5.75%
5.875% Senior Notes Due 2022
Debt Instrument [Line Items]
Interest rate on notes	5.875%	5.875%	5.875%	5.875%
9.25% Senior Notes Due 2026
Debt Instrument [Line Items]
Interest rate on notes	9.25%		9.25%
5.00% Senior Subordinated Notes Due 2022
Debt Instrument [Line Items]
Interest rate on notes	5.00%	5.00%	5.00%
5.00% Senior Subordinated Notes Due 2023
Debt Instrument [Line Items]
Interest rate on notes	5.00%		5.00%
5.75% Senior Subordinated Notes Due 2021
Debt Instrument [Line Items]
Interest rate on notes	5.75%	5.75%	5.75%
Notes Payable to Banks
Debt Instrument [Line Items]
Bank debt percentage	2.20%		2.20%