Fair Value Measurements - Fair Value of Other Financial Instruments Not Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Notes	$ 222,140	$ 208,414
Fair value, measurements, nonrecurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")	313,646	39,696
Convertible Notes	359,219	277,145
Fair value, measurements, nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")	313,646	39,696
Fair value, measurements, nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Notes	$ 359,219	$ 277,145