Fair Value Summary of Long-Term Debt with Fixed Interest Rates (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 1,110,000	$ 1,281,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt with fixed interest rates	854,000	1,145,469
Fair Value | 7.25% Senior Notes due 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt with fixed interest rates	234,000	307,500
Fair Value | 8.50% Senior Notes due 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt with fixed interest rates	620,000	837,969
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,075,000	1,075,000
Carrying Value | 7.25% Senior Notes due 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	300,000	300,000
Carrying Value | 8.50% Senior Notes due 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 775,000	$ 775,000