Exchangeable Senior Notes - Summary of Repurchase of Debt (Detail) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jun. 21, 2013
Debt Instrument [Line Items]
Total consideration paid for repurchase	$ 787,939	$ 1,020,144
Unamortized debt issuance costs	(4,808)		$ (6,620)
Exchangeable Senior Notes 2.375% due 2033 (the 2013 Notes)
Debt Instrument [Line Items]
Principal amount repurchased	49,259	13,786
Extinguishment of liability component	49,019	13,568
Reacquisition of equity component	31,251	6,285
Total consideration paid for repurchase	80,270	19,853
Extinguishment of liability component	(49,019)	(13,568)
Discount on exchangeable senior notes	(230)	(183)		$ (3,750)
Unamortized debt issuance costs	(10)	(35)		$ (1,672)
Gain/(loss) on repurchase	$ 0	$ 0

Debt instrument, repurchase of equity component.

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

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- Definition

Amount, after accumulated amortization, of debt discount.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Gross amount of debt extinguished.

+ References

No definition available.

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- Definition

Amount of gain (loss) from the difference between the repurchase price of a debt instrument initially issued by the entity and the net carrying amount of the debt at the time of its repurchase.

+ References

No definition available.

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- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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