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		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Earnings Per Share [Abstract]
Net income attributable to G-III (in dollars)	$ 81,625	$ 70,564	$ 62,666	$ 72,042
Basic net income per share:
Basic common shares	48,846	45,918	48,729	45,713
Basic net income per share (in dollars per share)	$ 1.67	$ 1.54	$ 1.29	$ 1.58
Diluted net income per share:
Basic common shares	48,846	45,918	48,729	45,713
Diluted restricted stock awards and stock options	682	984	681	1,234
Diluted common shares	49,528	46,902	49,410	46,947
Diluted net income per share (in dollars per share)	$ 1.65	$ 1.50	$ 1.27	$ 1.53