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Employee Benefit Plans - Additional Information (Detail) (USD $)
12 Months Ended
Jan. 31, 2013
Jan. 31, 2012
Jan. 31, 2011
Defined Benefit Plan Disclosure [Line Items]      
Employer matching percentage of employee contributions 50.00%    
Defined contribution plan, matching contributions $ 987,000 $ 869,000 $ 853,000
Maximum
     
Defined Benefit Plan Disclosure [Line Items]      
Defined contribution plan, employee contribution percentage for which employer contributes a matching contribution 3.00%