Indebtedness - Summary of 2024 Notes (Detail) - 2024 Convertible Notes [Member] - USD ($)	Dec. 31, 2017	Nov. 14, 2017
Debt Instrument [Line Items]
Par value of the 2024 Notes	$ 570,000,000	$ 570,000,000
Unamortized discounts	(158,890,000)
Debt issuance expenses	(10,449,000)
Net carrying value of convertible debt	400,661,000
Fair value of convertible debt	$ 619,641,000

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
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Fair value portion of borrowing which can be exchanged for a specified number of another security at the option of the issuer or the holder, for example, but not limited to, the entity's common stock.

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Face (par) amount of debt instrument at time of issuance.

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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