Fair Value Measurements and Other Financial Instruments - Carrying Amounts and Estimated Fair Values of Debt (Parenthetical) (Detail)	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
12% Senior Notes due February 2014
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	12.00%		12.00%
7.875% Senior Notes due June 2017
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	7.875%		7.875%
8.125% Senior Notes due September 2019
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	8.125%		8.125%
6.50% Senior Notes due December 2020
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	6.50%		6.50%
8.375% Senior Notes due September 2021
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	8.375%		8.375%
5.25% Senior Notes due April 2023
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	5.25%	5.25%	5.25%
6.875% Senior Notes due July 2033
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Debt interest rate	6.875%		6.875%