0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Net Carrying Amount of Equity Component (Detail) - 0.25% Convertible Senior Notes Due 2022 as Equity Component [Member] $ in Thousands	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Debt discount for conversion option	$ 106,006
Issuance costs	(2,854)
Net carrying amount	$ 103,152

0.25% Convertible Senior Notes, Convertible Note Hedge and Warrant - Schedule of Net Carrying Amount of Equity Component (Detail) - 0.25% Convertible Senior Notes Due 2022 as Equity Component [Member]
$ in Thousands

Sep. 30, 2017

USD ($)

Debt discount for conversion option

$ 106,006

Issuance costs

(2,854)

Net carrying amount

$ 103,152