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, 2013
Jan. 31, 2013
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost $ 125,531 $ 119,911
Gross Unrealized Gains 22 83
Gross Unrealized Losses      
Estimated Fair Value 125,553 119,994
Cash [Member]
   
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 109,721 104,109
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 109,721 104,109
Cash Equivalents [Member]
   
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 3,684 2,612
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 3,684 2,612
Cash and Cash Equivalents [Member]
   
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 113,405 106,721
Gross Unrealized Gains      
Gross Unrealized Losses      
Estimated Fair Value 113,405 106,721
US Government Agency Issues Short Term [Member]
   
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 5,018 6,043
Gross Unrealized Gains 4 61
Gross Unrealized Losses      
Estimated Fair Value 5,022 6,104
US Government Agency Issues Long Term [Member]
   
Schedule of Available-for-Sale Securities [Line Items]    
Amortized Cost 7,108 7,147
Gross Unrealized Gains 18 22
Gross Unrealized Losses      
Estimated Fair Value $ 7,126 $ 7,169