Fair Value Measurements - Available-for-Sale Securities Measured at Fair Value (Parenthetical) (Detail)	Sep. 30, 2014	Dec. 31, 2013
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%
Fair Value, Measurements, Recurring [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed annual rate of interest	8.00%	8.00%
Fair Value, Measurements, Recurring [Member] | Convertible Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument stated interest rate	3.875%	3.875%