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Activity of sales Return Reserve (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Jan. 31, 2017
Jan. 31, 2016
Jan. 31, 2015
Revenue Recognition, Allowances [Line Items]      
Balance at beginning of year $ 24,385 $ 19,804 $ 17,089
Additions 105,909 96,707 80,390
Deductions (105,412) (92,126) (77,675)
Balance at end of year $ 24,882 $ 24,385 $ 19,804