Carrying Value of Convertible Senior Notes (Parenthetical) (Detail) - 2.125% Convertible Senior Notes due 2021	9 Months Ended
Sep. 30, 2018	May 24, 2016
Debt Instrument [Line Items]
Notes, interest rate	2.125%	2.125%
Notes, due date	Jun. 01, 2021

Contractual interest rate for funds borrowed, under the debt agreement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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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.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
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