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Line of Credit Facility - Additional Information (Detail) (USD $)
 6 Months Ended
Jul. 31, 2012
Year
Line of Credit Facility [Line Items]  
Line of credit facility, extension of term per amendment, number of years 3
Line Of Credit Facility
  
Line of Credit Facility [Line Items]  
Outstanding letters of credit and stand-by letters of credit 68,818,000
Available credit, including accordion feature 106,182,000
Minimum
  
Line of Credit Facility [Line Items]  
Interest rate on cash advances in addition to LIBOR 0.50%
Minimum | Amendment
  
Line of Credit Facility [Line Items]  
Increase in available credit limit 100,000,000
Maximum
  
Line of Credit Facility [Line Items]  
Interest rate on cash advances in addition to LIBOR 1.50%
Maximum | Amendment
  
Line of Credit Facility [Line Items]  
Increase in available credit limit 175,000,000