Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
Apr. 30, 2013
Jan. 31, 2013
Financial assets:    
Cash $ 105,525 $ 104,109
Money market accounts 3,664 [1] 2,612 [1]
Available for sale marketable securities:    
U.S. government agency issues - Current 5,037 6,104
Non-current marketable securities:    
U.S. government agency issues - Non current 7,154 7,169
Total 121,380 119,994
Other liabilities:    
Acquisition-related consideration 2,388 [2] 5,656 [2]
Fair Value, Inputs, Level 1 [Member]
    
Financial assets:    
Cash 105,525 104,109
Money market accounts 3,664 [1] 2,612 [1]
Available for sale marketable securities:    
U.S. government agency issues - Current 5,037 6,104
Non-current marketable securities:    
U.S. government agency issues - Non current 7,154 7,169
Total 121,380 119,994
Other liabilities:    
Acquisition-related consideration 0 [2] 0 [2]
Fair Value, Inputs, Level 2 [Member]
    
Financial assets:    
Cash 0 0
Money market accounts 0 [1] 0 [1]
Available for sale marketable securities:    
U.S. government agency issues - Current 0 0
Non-current marketable securities:    
U.S. government agency issues - Non current 0 0
Total 0 0
Other liabilities:    
Acquisition-related consideration 0 [2] 0 [2]
Fair Value, Inputs, Level 3 [Member]
    
Financial assets:    
Cash 0 0
Money market accounts 0 [1] 0 [1]
Available for sale marketable securities:    
U.S. government agency issues - Current 0 0
Non-current marketable securities:    
U.S. government agency issues - Non current 0 0
Total 0 0
Other liabilities:    
Acquisition-related consideration $ 2,388 [2] $ 5,656 [2]
[1] Money market funds and U.S. government agency securities, included in cash and cash equivalents on the accompanying consolidated balance sheet, are valued at quoted market prices for identical instruments in active markets.
[2] The fair value of our contingent consideration arrangement is determined based on our evaluation as to the probability and amount of any earn-out that will be achieved based on expected future performance by the acquired entity, as well as the fair value of fixed purchase price.