Net Income per Common Share - Reconciliation between basic and diluted net income per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Net Income (Loss) per Common Share
Net income attributable to G-III Apparel Group, Ltd.	$ 26,321	$ (39,295)
Basic net income (loss) per share:
Basic common shares	48,377	48,025
Basic net income (loss) per share (in dollars per share)	$ 0.54	$ (0.82)
Diluted net income (loss) per share:
Basic common shares	48,377	48,025
Diluted restricted stock awards and stock options	1,133
Diluted common shares	49,510	48,025
Diluted net income (loss) per share (in dollars per share)	$ 0.53	$ (0.82)