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Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands | May 02, 2017 | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Convertible senior notes principal amount |  | $ 517,500 | $ 517,500
2.25% Convertible Senior Notes due 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Convertible senior notes principal amount | $ 517,500 |  |
Convertible senior notes interest percentage | 2.25% |  |
Convertible senior notes convertible latest date | May 15, 2024 |  |
Convertible senior notes term | 7 years |  |
2.25% Convertible Senior Notes due 2024 | Significant Other Observable Inputs (Level 2) |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument fair value |  | $ 708,700 | $ 616,100

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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