Fair Value Measurements and Other Financial Instruments - Carrying Amounts and Estimated Fair Values of Debt (Parenthetical) (Detail)	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2012	Nov. 30, 2014	Oct. 16, 2014	Nov. 30, 2012	Mar. 31, 2013
12% Senior Notes Due February 2014 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	12.00%	12.00%	12.00%
8.125% Senior Notes Due September 2019 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt interest rate	8.125%	8.125%		8.125%
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%			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%		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%					5.25%
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%		5.125%
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%