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Convertible Senior Notes - Additional Information (Detail) $ / shares in Units, shares in Millions |  | 6 Months Ended |
--- | --- | --- | ---
May 02, 2017 USD ($) | Jun. 30, 2019 USD ($) d $ / shares shares | 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 interest rate | 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 |
Debt instrument conversion obligation period of consecutive trading days. |  | 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 |
Threshold common stock trading days | d |  | 20 |
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 |  | 7 years |
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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- Definition The percentage of excess of the price paid for the convertible note over the closing stock price on the closing date of the convertible note. + References No definition available. + Details
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- Definition The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 + Details
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- Definition The rate of interest that was being paid on the original debt issue that is being converted in the noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586 + Details
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