Impact of Adjustments to Redeemable Non-controlling Interest on Earnings Per Share Calculation (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net loss from continuing operations attributable to Iconix Brand Group, Inc.	$ 24,743	$ (550,571)	$ (13,852)	$ 4,402	$ (293,909)	$ 14,180	$ 10,602	$ 14,629	$ (535,278)	$ (254,498)	$ (201,659)
Accretion of redeemable non-controlling interest									(5,589)
Net loss attributable to Iconix Brand Group, Inc. after accretion of redeemable non-controlling interest									(540,867)
Net income from discontinued operations attributable to Iconix Brand Group, Inc.	$ (656)	$ (2,130)	$ 57,493	$ (8,682)	$ (3,639)	$ 1,036	$ 980	$ 3,987	46,025	$ 2,364	$ 15,145
Net loss attributable to Iconix Brand Group, Inc.									$ (494,842)
(Loss) earnings per share - basic:
Continuing operations	$ 0.40	$ (9.64)	$ (0.26)	$ 0.06	$ (5.23)	$ 0.26	$ 0.22	$ 0.30	$ (9.47)	$ (4.86)	$ (4.18)
Discontinued operations	(0.01)	(0.04)	1.01	(0.15)	(0.06)	0.02	0.02	0.08	0.81	0.05	0.31
(Loss) earnings per share - basic:									(8.66)	(4.82)	(3.86)
(Loss) earnings per share - diluted:
Continuing operations	0.40	(9.64)	(0.26)	0.06	(5.23)	0.25	0.21	0.29	(9.47)	(4.86)	(4.18)
Discontinued operations	$ (0.01)	$ (0.04)	$ 1.00	$ (0.15)	$ (0.06)	$ 0.02	$ 0.02	$ 0.08	0.81	0.05	0.31
(Loss) earnings per share - diluted									$ (8.66)	$ (4.82)	$ (3.86)
Weighted average number of common shares outstanding:
Basic									57,112	52,338	48,293
Diluted									57,112	52,338	48,293