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Fair Value Measurements - Schedule of Fair Value Information for Financial Assets and Liabilities Carried on Balance Sheet (Parenthetical) (Detail)
Jun. 30, 2015
Dec. 31, 2014
Senior Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed annual rate of interest 8.00%  
Convertible Senior Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt instrument stated interest rate 3.875%  
Portion at Other than Fair Value Measurement [Member] | Senior Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fixed annual rate of interest 8.00% 8.00%
Portion at Other than Fair Value Measurement [Member] | Convertible Senior Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Debt instrument stated interest rate 3.875% 3.875%