Fair Value Disclosures - Fair Value of Other Financial Instruments Not Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Notes	$ 225,007	$ 222,140
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")	379,600	313,646
Fair value, measurements, nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Notes	472,974	359,219
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")	379,600	313,646
Convertible Notes	$ 472,974	$ 359,219