Convertible Notes, Net - Summary of Details of Net Book Value of Convertible Note (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Deferred financing costs	$ (20,497)	$ (16,681)
Net book value	780,951	563,911
Convertible Senior Note [Member]
Debt Instrument [Line Items]
Face Value	794,828	575,000
Unamortized discount	(12,956)	(10,279)
Deferred financing costs	(921)	(810)
Net book value	$ 780,951	$ 563,911

Including the current and noncurrent portions, carrying value as of the balance sheet date of a written promise to pay a note, initially due after one year or beyond the operating cycle if longer, which can be exchanged for a specified amount of one or more securities (typically common stock), at the option of the issuer or the holder.

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