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Debt - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended
Feb. 28, 2017
Jul. 31, 2016
Apr. 30, 2017
Apr. 30, 2016
Jan. 31, 2017
Mar. 31, 2013
Debt Instrument [Line Items]            
Amount outstanding     $ 0      
Debt interest expense     $ 13,397,000 $ 10,068,000    
Revolving Credit Facility            
Debt Instrument [Line Items]            
Maximum borrowing capacity   $ 1,000,000,000.0        
Debt default interest rate above applicable interest rate for overdue principal   2.00%        
Debt default interest rate above applicable interest rate for base rate loans and other   2.00%        
Pay down of debt $ 200,000,000          
Revolving Credit Facility | Minimum            
Debt Instrument [Line Items]            
Commitment fee percentage   0.125%        
Revolving Credit Facility | Minimum | Base Rate            
Debt Instrument [Line Items]            
Basis spread on variable rate   0.00%        
Revolving Credit Facility | Minimum | Adjusted LIBOR            
Debt Instrument [Line Items]            
Basis spread on variable rate   1.00%        
Revolving Credit Facility | Maximum            
Debt Instrument [Line Items]            
Commitment fee percentage   0.25%        
Revolving Credit Facility | Maximum | Base Rate            
Debt Instrument [Line Items]            
Basis spread on variable rate   0.75%        
Revolving Credit Facility | Maximum | Adjusted LIBOR            
Debt Instrument [Line Items]            
Basis spread on variable rate   1.75%        
Convertible Debt | 0.25% Convertible Senior Notes due April 1, 2018            
Debt Instrument [Line Items]            
Face amount of debt           $ 1,150,000,000
Contractual interest rate     0.25%     0.25%
Consecutive trading days threshold     20 days      
Consecutive trading days threshold, total     30 days      
Stock price trigger     130.00%      
Notes price trigger     98.00%      
Purchase price upon fundamental change     100.00%      
Estimated fair value of Company's senior notes     $ 1,500,000,000      
Fair value debt basis amount     $ 100      
Closing prices of Company's common stock (in dollars per share)     $ 86.12      
If-converted value in excess of principal     $ 340,600,000      
Notes Payable to Banks | 0.25% Convertible Senior Notes due April 1, 2018            
Debt Instrument [Line Items]            
Contractual interest rate     0.25%   0.25%  
Notes Payable to Banks | Term Loan Credit Agreement            
Debt Instrument [Line Items]            
Face amount of debt   $ 500,000,000.0 $ 500,000,000.0      
Weighted average interest rate     2.00%      
Accrued interest     $ 400,000      
Debt default interest rate above applicable interest rate for overdue principal   2.00%        
Debt default interest rate above applicable interest rate for base rate loans and other   2.00%        
Notes Payable to Banks | Term Loan Credit Agreement | Minimum | Base Rate            
Debt Instrument [Line Items]            
Basis spread on variable rate   0.00%        
Notes Payable to Banks | Term Loan Credit Agreement | Minimum | Adjusted LIBOR            
Debt Instrument [Line Items]            
Basis spread on variable rate   1.00%        
Notes Payable to Banks | Term Loan Credit Agreement | Maximum | Base Rate            
Debt Instrument [Line Items]            
Basis spread on variable rate   0.75%        
Notes Payable to Banks | Term Loan Credit Agreement | Maximum | Adjusted LIBOR            
Debt Instrument [Line Items]            
Basis spread on variable rate   1.75%        
Mortgage Loan | 50 Fremont Street            
Debt Instrument [Line Items]            
Contractual interest rate     3.75%      
Loan assumed on 50 Fremont     $ 200,000,000      
Debt interest expense     $ 1,900,000 $ 1,900,000