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Convertible Senior Notes - Additional Information (Detail)
$ / shares in Units, shares in Millions
3 Months Ended
May 02, 2017
USD ($)
Mar. 31, 2019
USD ($)
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%