Fair Value Measurements and Other Financial Instruments - Carrying Amounts and Estimated Fair Values of Debt (Parenthetical) (Detail)	Jun. 30, 2015	Dec. 31, 2014
6.50% Senior Notes Due December 2020 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	6.50%	6.50%
8.375% Senior Notes Due September 2021 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	8.375%	8.375%
4.875% Senior Notes due December 2022 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	4.875%	4.875%
5.25% Senior Notes Due April 2023 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	5.25%	5.25%
4.50% Senior Notes due September 2023 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	4.50%	4.50%
5.125% Senior Notes due December 2024 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	5.125%	5.125%
5.50% Senior Notes due September 2025 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	5.50%	5.50%
6.875% Senior Notes Due July 2033 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	6.875%	6.875%