Fair Value Measurements - Carrying Amounts and Fair Values of Financial Instruments (Parenthetical) (Detail)	Sep. 30, 2013	Dec. 31, 2012
7.25% Senior Subordinated notes due 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	7.25%	7.25%
8.00% Senior Subordinated notes due 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	8.00%	8.00%
6.75% Senior Subordinated notes due 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	6.75%	6.75%
5.75% Senior Subordinated Notes due 2021
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	5.75%	5.75%
5.00% Senior Subordinated notes due 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	5.00%	5.00%
5.00% senior subordinated notes due 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	5.00%	5.00%