v3.7.0.1
Convertible Senior Notes, Net (Detail)
$ / shares in Units, shares in Millions
3 Months Ended
Apr. 30, 2017
USD ($)
trading_day
$ / shares
shares
Apr. 30, 2016
USD ($)
Jan. 31, 2017
USD ($)
Jun. 30, 2013
USD ($)
2018 Notes        
Debt Instrument [Line Items]        
Contractual interest rate 0.75%     0.75%
Convertible senior notes, principal amount $ 350,000,000   $ 350,000,000 $ 350,000,000
Liability issuance costs 7,000,000      
Equity issuance costs 2,000,000      
Amortization expense for liability issuance costs $ 352,000 $ 352,000    
Remaining life of the Notes 14 months      
Effective interest rates of the liability components 5.75%      
2020 Notes        
Debt Instrument [Line Items]        
Contractual interest rate 1.50%     1.50%
Convertible senior notes, principal amount $ 250,000,000   $ 250,000,000 $ 250,000,000
Liability issuance costs 5,000,000      
Equity issuance costs 2,000,000      
Amortization expense for liability issuance costs $ 168,000 $ 167,000    
Remaining life of the Notes 38 months      
Effective interest rates of the liability components 6.25%      
Shares related to the convertible senior notes        
Debt Instrument [Line Items]        
Repurchase of notes percentage 100.00%      
Exercise price of warrants (in dollars per share) | $ / shares $ 107.96      
Proceeds from sale of warrants $ 93,000,000      
Shares related to the convertible senior notes | Employee Stock Option        
Debt Instrument [Line Items]        
Shares covered by each purchased options or warrants (in shares) | shares 7.3      
Aggregate amount for Purchased Options $ 144,000,000      
Warrants expires in July 2018        
Debt Instrument [Line Items]        
Shares covered by each purchased options or warrants (in shares) | shares 4.2      
Warrants expires in July 2020        
Debt Instrument [Line Items]        
Shares covered by each purchased options or warrants (in shares) | shares 3.1      
Class A | 2018 Notes        
Debt Instrument [Line Items]        
Initial conversion rate 12.0075      
Principal amount converted into Class A Common Stock $ 1,000      
Initial conversion price (in dollars per share) | $ / shares $ 83.28      
Class A | 2020 Notes        
Debt Instrument [Line Items]        
Initial conversion rate 12.2340      
Principal amount converted into Class A Common Stock $ 1,000      
Initial conversion price (in dollars per share) | $ / shares $ 81.74      
Debt Conversion, Option One | Shares related to the convertible senior notes        
Debt Instrument [Line Items]        
Threshold trading days (in trading days) | trading_day 20      
Threshold consecutive trading days 30 days      
Threshold percentage of conversion price 130.00%      
Debt Conversion, Option Two | Shares related to the convertible senior notes        
Debt Instrument [Line Items]        
Threshold trading days (in trading days) | trading_day 5      
Threshold consecutive trading days 5 days      
Debt Conversion, Option Two | Shares related to the convertible senior notes | Maximum        
Debt Instrument [Line Items]        
Threshold percentage of conversion price 98.00%