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Marketable Securities (Unrealized Losses And Fair Value Of Marketable Securities) (Details) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2012
Jan. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value $ 58,701 $ 171,846
Less Than 12 Months, Unrealized Losses (111) (723)
12 Months or Greater, Fair Value 23,151 29,462
12 Months or Greater, Unrealized Losses (2,785) (3,788)
Total, Fair Value 81,852 201,308
Total, Unrealized Losses (2,896) (4,511)
Corporate Bonds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value 45,089  
Less Than 12 Months, Unrealized Losses (100)  
Total, Fair Value 45,089  
Total, Unrealized Losses (100)  
Municipal And Pre-Refunded Municipal Bonds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value 9,985 103,090
Less Than 12 Months, Unrealized Losses (9) (567)
12 Months or Greater, Fair Value 2,954  
12 Months or Greater, Unrealized Losses (7)  
Total, Fair Value 12,939 103,090
Total, Unrealized Losses (16) (567)
Auction Rate Securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
12 Months or Greater, Fair Value 20,197 29,462
12 Months or Greater, Unrealized Losses (2,778) (3,788)
Total, Fair Value 20,197 29,462
Total, Unrealized Losses (2,778) (3,788)
Treasury Bills [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value 1,039  
Total, Fair Value 1,039  
Certificate Of Deposit [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value 1,489  
Less Than 12 Months, Unrealized Losses (1)  
Total, Fair Value 1,489  
Total, Unrealized Losses (1)  
Federal Government Agencies [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value 1,099 1,397
Less Than 12 Months, Unrealized Losses (1) (2)
Total, Fair Value 1,099 1,397
Total, Unrealized Losses (1) (2)
FDIC Insured Corporate Bonds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Less Than 12 Months, Fair Value   67,359
Less Than 12 Months, Unrealized Losses   (154)
Total, Fair Value   67,359
Total, Unrealized Losses   $ (154)