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Line Of Credit Facility (Details) (USD $)
 6 Months Ended 0 Months Ended 0 Months Ended
Jul. 31, 2011
Jul. 31, 2011
Maximum [Member]
Jul. 31, 2011
Minimum [Member]
Apr. 25, 2011
Line Of Credit Facility [Member]
Jul. 31, 2011
Line Of Credit Facility [Member]
Apr. 25, 2011
Amendment [Member]
Line of credit facility, extension of term per amendment, number of years three          
Increase in available credit limit       $ 100,000,000   $ 175,000,000
Interest rate on cash advances in addition to LIBOR   1.50% 0.50%      
Remaining borrowings under the credit facility         0  
Outstanding letters of credit and stand-by letters of credit         63,131,000  
Available credit including accordion feature         $ 111,869,000