Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Summary of Available-for-Sale Securities (Detail)

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Fair Value Measurements - Summary of Available-for-Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Jul. 31, 2014
Jan. 31, 2014
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost $ 110,865 $ 128,085
Gross Unrealized Gains 12 18
Gross Unrealized Losses (5)   
Estimated Fair Value 110,872 128,103
Cash [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 95,047 112,271
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 95,047 112,271
Cash Equivalents [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 1,508 3,463
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 1,508 3,463
Cash and Cash Equivalents [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 96,555 115,734
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 96,555 115,734
U.S. Treasury Notes and Bonds - Short Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 2,510 3,540
Gross Unrealized Gains 1 5
Gross Unrealized Losses     
Estimated Fair Value 2,511 3,545
U.S. Treasury Notes and Bonds - Long Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 2,011  
Gross Unrealized Gains     
Gross Unrealized Losses (5)  
Estimated Fair Value 2,006  
U.S. Government Agency Issues Short Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 3,520 2,005
Gross Unrealized Gains 7 5
Gross Unrealized Losses      
Estimated Fair Value 3,527 2,010
U.S. Government Agency Issues Long Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 6,269 6,806
Gross Unrealized Gains 4 8
Gross Unrealized Losses      
Estimated Fair Value $ 6,273 $ 6,814