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Property and Equipment - Additional Information (Detail) (USD $)
12 Months Ended
Jan. 31, 2013
Jan. 31, 2012
Jan. 31, 2011
Property, Plant and Equipment [Line Items]      
Fixed asset disposals $ 447,000 $ 523,000  
Depreciation expense $ 8,700,000 $ 6,600,000 $ 4,400,000