Net Income (Loss) 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		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Abstract]
Net income (loss) attributable to G-III (in dollars)	$ (8,568)	$ (1,293)	$ (18,959)	$ 1,478
Basic net income (loss) per share:
Basic common shares	48,689	45,667	48,669	45,601
Basic net income (loss) per share (in dollars per share)	$ (0.18)	$ (0.03)	$ (0.39)	$ 0.03
Diluted net income (loss) per share:
Basic common shares	48,689	45,667	48,669	45,601
Diluted restricted stock awards and stock options				1,366
Diluted common shares	48,689	45,667	48,669	46,967
Diluted net income (loss) per share (in dollars per share)	$ (0.18)	$ (0.03)	$ (0.39)	$ 0.03