Annual report pursuant to Section 13 and 15(d)

Investments in Marketable Securities - Summary of Available-for-Sale Securities (Detail)

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Investments in Marketable Securities - Summary of Available-for-Sale Securities (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2014
Jan. 31, 2013
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost $ 128,085 $ 119,910
Gross Unrealized Gains 18 30
Gross Unrealized Losses      
Estimated Fair Value 128,103  
Estimated Fair Value   119,940
Cash [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 112,271 104,109
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 112,271  
Estimated Fair Value   104,109
Cash Equivalents [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 3,463 2,612
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 3,463  
Estimated Fair Value   2,612
Cash and Cash Equivalents [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 115,734 106,721
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 115,734  
Estimated Fair Value   106,721
U.S. Treasury Notes and Bonds - Short Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 3,540 2,015
Gross Unrealized Gains 5 1
Gross Unrealized Losses     
Estimated Fair Value 3,545  
Estimated Fair Value   2,016
U.S. Treasury Notes and Bonds - Long Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost   2,064
Gross Unrealized Gains   7
Gross Unrealized Losses     
Estimated Fair Value   2,071
U.S. Government Agency Issues Short Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 2,005 4,027
Gross Unrealized Gains 5 7
Gross Unrealized Losses      
Estimated Fair Value 2,010  
Estimated Fair Value   4,034
U.S. Government Agency Issues Long Term [Member]
    
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 6,806 5,083
Gross Unrealized Gains 8 15
Gross Unrealized Losses     
Estimated Fair Value 6,814  
Estimated Fair Value   $ 5,098