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Convertible Senior Notes - Additional Information (Detail)
$ / shares in Units, $ in Thousands
12 Months Ended
May 02, 2017
USD ($)
Dec. 31, 2017
USD ($)
d
$ / shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]        
Convertible senior notes principal amount   $ 517,500    
Proceeds from Senior Convertible Notes   $ 502,781 $ 0 $ 0
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 interest rate 2.25%      
Proceeds from Senior Convertible Notes $ 502,800      
Threshold common stock trading days | d   20    
Threshold consecutive common stock trading days | d   30    
Threshold percentage of common stock price trigger   130.00%    
Minimum percentage of common stock price trigger   98.00%    
Conversion Observation Period   25 days    
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%    
Convertible senior notes redemption rate   100.00%    
Convertible senior note carrying value of the liability component   $ 368,300    
Convertible senior note assumed borrowing rate   7.50%    
Convertible senior note carrying value of the equity component   $ 149,200    
Convertible senior notes   7 years    
Transaction cost related to issuance of convertible senior note   $ 14,700