Fair Value Measurements - Carrying Amounts and Fair Values of Financial Instruments (Parenthetical) (Detail) (Senior Subordinated Notes)	Sep. 30, 2014	Dec. 31, 2013
8.00% 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% 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% 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% 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% Notes Due 2023
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior subordinated notes	5.00%	5.00%