Fair Value Measurements - Carrying Amounts and Fair Values of Financial Instruments (Parenthetical) (Detail)	Sep. 30, 2015	May. 31, 2015	Dec. 31, 2014
Senior Notes | 4.875% Senior Notes Due 2025
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on notes	4.875%	4.875%	4.875%
Senior Subordinated Notes | 6.75% Senior Subordinated Notes Due 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on notes	6.75%	6.75%	6.75%
Senior Subordinated Notes | 5.75% Senior Subordinated Notes Due 2021
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on notes	5.75%		5.75%
Senior Subordinated Notes | 5.00% Senior Subordinated Notes Due 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on notes	5.00%		5.00%
Senior Subordinated Notes | 5.00% Senior Subordinated Notes Due 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on notes	5.00%		5.00%