Fair Value Disclosures - Fair Value of Other Financial Instruments Not Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")	$ 157,968	$ 71,301	$ 115,557	$ 70,136
Convertible Notes	205,173	196,007
Fair value [Member] | Fair value, measurements, nonrecurring [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")	52,130	22,608
Convertible Notes	261,709	234,813
Level 1 [Member] | Fair value, measurements, nonrecurring [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")	52,130	22,608
Convertible Notes
Level 2 [Member] | Fair value, measurements, nonrecurring [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")
Convertible Notes	261,709	234,813
Level 3 [Member] | Fair value, measurements, nonrecurring [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Bank deposits (included in "Cash and cash equivalents")
Convertible Notes