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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)
9 Months Ended 12 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Debt Instrument [Line Items]    
Carrying value of warehouse facility liability $ 124,400,000  
2018 Notes [Member]    
Debt Instrument [Line Items]    
Estimated fair value of notes 1,350,000,000 $ 1,220,000,000
Principal amount of convertible senior notes 659,762,000 659,762,000
2019 Notes [Member]    
Debt Instrument [Line Items]    
Estimated fair value of notes 890,100,000 852,200,000
Principal amount of convertible senior notes 920,000,000 920,000,000
2021 Notes [Member]    
Debt Instrument [Line Items]    
Estimated fair value of notes 1,300,000,000 1,250,000,000
Principal amount of convertible senior notes 1,380,000,000 1,380,000,000
Maximum [Member]    
Debt Instrument [Line Items]    
Unrealized gains (losses) on financial assets $ 1,000,000 $ 1,000,000