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Activity of Allowance for Doubtful Accounts (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Jan. 31, 2013
Jan. 31, 2012
Jan. 31, 2011
Receivables And Related Allowances [Line Items]      
Balance at beginning of year $ 1,614 $ 1,015 $ 1,284
Additions 5,019 3,920 2,397
Deductions (4,952) (3,321) (2,666)
Balance at end of year $ 1,681 $ 1,614 $ 1,015