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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended 12 Months Ended 3 Months Ended
Jan. 31, 2014
Jan. 31, 2013
Jan. 31, 2012
Jan. 31, 2014
Long Term Investments
Jan. 31, 2013
Long Term Investments
Jan. 31, 2014
Accumulated Other Comprehensive Income (Loss)
Jan. 31, 2013
Accumulated Other Comprehensive Income (Loss)
Jan. 31, 2012
Accumulated Other Comprehensive Income (Loss)
Jan. 31, 2014
Furniture and Fixtures
Jan. 31, 2014
Leasehold Improvements
Jan. 31, 2014
Equipment
Minimum
Jan. 31, 2014
Equipment
Maximum
Jan. 31, 2014
Building
Apr. 30, 2013
Auction Rate Securities
Jan. 31, 2013
Auction Rate Securities
Jan. 31, 2013
Auction Rate Securities
Long Term Investments
Summary Of Significant Accounting Policies [Line Items]                                
Proceeds from sale of available-for-sale securities                           $ 4,580    
Amortized cost of available-for-sale securities 647,483 378,393   365,809 150,107                     4,925
Estimated fair value of available-for-sale securities 648,235 378,071   366,422 149,585                   4,330 4,330
Average useful life (in years)                 5 years   3 years 10 years 39 years      
Depreciable life (in years)                   Lesser of the lease term or useful life for leasehold improvements            
Advertising costs reported as prepaid expenses 2,067 2,716                            
Advertising expense 91,615 81,944 71,684                          
Foreign currency translation losses 7,194 1,455 (2,285)     (1,388) (8,582)                  
Unrealized gains / (losses) on marketable securities, net of tax           420 (200)                  
Change in unrealized gains / (losses) on marketable securities, tax           $ (378) $ (672) $ (556)