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Line of Credit Facility - Additional Information (Detail) (USD $)
 12 Months Ended
Jan. 31, 2013
Minimum
  
Line of Credit Facility [Line Items]  
Interest rate on cash advances in addition to LIBOR 0.50%
Maximum
  
Line of Credit Facility [Line Items]  
Interest rate on cash advances in addition to LIBOR 1.50%
Amendment | Minimum
  
Line of Credit Facility [Line Items]  
Increase in available credit limit $ 100,000,000
Amendment | Maximum
  
Line of Credit Facility [Line Items]  
Increase in available credit limit 175,000,000
Line Of Credit Facility
  
Line of Credit Facility [Line Items]  
Outstanding letters of credit and stand-by letters of credit 58,305,000
Available credit including accordion feature $ 116,695,000
Revolving Credit Facility
  
Line of Credit Facility [Line Items]  
Line of credit facility, extension of term per amendment, number of years Three