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0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Net Carrying Amount of Liability Component (Detail)
$ in Thousands
Sep. 30, 2017
USD ($)
Debt Instrument [Line Items]  
Net carrying amount $ 293,563
0.25% Convertible Senior Notes Due 2022 as Liability Component [Member]  
Debt Instrument [Line Items]  
Principal 400,000
Unamortized debt discount (99,042)
Unamortized issuance costs (7,395)
Net carrying amount $ 293,563