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Convertible Senior Notes - Additional Information (Detail) $ / shares in Units, shares in Millions |  | 9 Months Ended |
--- | --- | --- | ---
May 02, 2017 USD ($) d $ / shares shares | Sep. 30, 2019 USD ($) | Dec. 31, 2018 USD ($)
Debt Instrument [Line Items] |  |  |
Convertible senior notes principal amount |  | $ 517,500,000 | $ 517,500,000
2.25% Convertible Senior Notes due 2024 |  |  |
Debt Instrument [Line Items] |  |  |
Convertible senior notes principal amount | $ 517,500,000 |  |
Convertible senior notes interest percentage | 2.25% |  |
Convertible senior notes convertible latest date | May 15, 2024 |  |
Proceeds from Senior Convertible Notes | $ 502,800,000 |  |
Threshold common stock trading days | d | 20 |  |
Threshold consecutive common stock trading days | d | 30 |  |
Threshold percentage of common stock price trigger | 130.00% |  |
Debt instrument conversion obligation number of consecutive business days after consecutive trading day period | 5 days |  |
Principal amount on conversion rate | $ 1,000 |  |
Minimum percentage of common stock price trigger | 98.00% |  |
Debt instrument convertible trading days during observation period | 30 days |  |
Conversion Observation Period | 25 days |  |
Debt instrument conversion value description | The conversion value is the sum of the daily conversion value which is the product of the effective conversion rate divided by 25 days and the daily volume weighted average price (VWAP) of our common stock. |  |
Debt instrument conversion share amount description | The “share amount” is the cumulative “daily share amount” during the observation period, which is calculated by dividing the daily VWAP into the difference between the daily conversion value (i.e., conversion rate x daily VWAP) and $1,000. |  |
Convertible senior notes convertible in to shares | 0.00131711 |  |
Convertible senior notes conversion price | $ / shares | $ 75.92 |  |
Market Price of Common stock | $ / shares | $ 53.28 |  |
Convertible senior note premium | 42.50% |  |
Shares issued to settle notes at initial conversion rate | shares | 6.8 |  |
Convertible senior notes redemption rate | 100.00% |  |
Convertible senior note carrying value of the liability component | $ 368,300,000 |  |
Convertible senior note assumed borrowing rate | 7.50% |  |
Convertible senior note carrying value of the equity component | $ 149,200,000 |  |
Convertible senior notes term | 7 years |  |
Discount on liability component, remaining amortization period |  | 4 years 8 months 12 days |
Transaction cost related to issuance of convertible senior note | $ 14,700,000 |  |
Debt instrument events of default percentage of principal and accrued and unpaid interest due and payable upon default | 100.00% |  |

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