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SIGNIFICANT ACCOUNTING POLICIES - Reconciliation between Basic and Diluted Net Income per Share (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Jan. 31, 2021
Oct. 31, 2020
Jul. 31, 2020
Apr. 30, 2020
Jan. 31, 2020
Oct. 31, 2019
Jul. 31, 2019
Apr. 30, 2019
Jan. 31, 2021
Jan. 31, 2020
Jan. 31, 2019
Accounting Policies [Abstract]                      
Net income (loss)                 $ 23,523 $ 143,837 $ 138,067
Net income attributable to G-III Apparel Group, Ltd. $ 14,642 $ 63,174 $ (14,976) $ (39,295) $ 25,288 $ 95,387 $ 11,119 $ 12,043 $ 23,545 $ 143,837 $ 138,067
Basic net income (loss) per share:                      
Basic common shares                 48,242 48,209 49,140
Net income (loss) per common share (in dollar per shares) $ 0.30 $ 1.31 $ (0.31) $ (0.82) $ 0.53 $ 2.00 $ 0.23 $ 0.25 $ 0.49 $ 2.98 $ 2.81
Diluted net income (loss) per share:                      
Basic common shares                 48,242 48,209 49,140
Diluted restricted stock awards and stock options                 539 686 1,134
Diluted common shares                 48,781 48,895 50,274
Diluted net income (loss) per share (in dollars per share) $ 0.30 $ 1.29 $ (0.31) $ (0.82) $ 0.52 $ 1.97 $ 0.23 $ 0.24 $ 0.48 $ 2.94 $ 2.75