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Line of Credit Facility - Additional Information (Detail) (USD $)
 9 Months Ended
Oct. 31, 2012
Line of Credit Facility [Line Items]  
Line of credit facility, extension of term per amendment, number of years 3 years
Line of credit facility, maximum borrowing capacity $ 100,000,000
Outstanding letters of credit and stand-by letters of credit 60,461,000
Available credit, including accordion feature 114,539,000
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
  
Line of Credit Facility [Line Items]  
Line of credit facility, maximum borrowing capacity $ 175,000,000