XML 61 R49.htm IDEA: XBRL DOCUMENT v3.10.0.1
Fair Value Measurements - Narrative (Detail) - USD ($)
9 Months Ended
Oct. 31, 2018
Jan. 31, 2018
Sep. 30, 2017
Jun. 30, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Closing price of company's common stock, dollars per share $ 133.02      
0.75% Convertible senior notes        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Convertible senior notes, principal amount $ 0 $ 350,000,000   $ 350,000,000
Contractual interest rate 0.75%     0.75%
1.50% Convertible senior notes        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Convertible senior notes, principal amount $ 249,997,000 $ 250,000,000   $ 250,000,000
Contractual interest rate 1.50%     1.50%
If-converted value in excess of principal $ 157,000,000      
0.25% Convertible senior notes        
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]        
Convertible senior notes, principal amount     $ 1,150,000,000.00  
Contractual interest rate 0.25%   0.25%  
If-converted value less than principal $ 110,000,000