Carrying Amount and Estimated Fair Values of Debt (Parenthetical) (Detail)	Sep. 30, 2012	Dec. 31, 2011
5.625 % Senior Notes due July 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt interest rate	5.625%	5.625%
12% Senior Notes due February 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt interest rate	12.00%	12.00%
7.875% Senior Notes due June 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt interest rate	7.875%	7.875%
8.125% Senior Notes due 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt interest rate	8.125%	8.125%
8.375% Senior Notes due 2021 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt interest rate	8.375%	8.375%
6.875% Senior Notes due July 2033 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Debt interest rate	6.875%	6.875%