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Activity of sales Return Reserve (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Revenue Recognition Allowances [Abstract]      
Balance at beginning of year $ 24,882 $ 24,385 $ 19,804
Additions 115,353 105,909 96,707
Deductions (111,333) (105,412) (92,126)
Balance at end of year $ 28,902 $ 24,882 $ 24,385