Schedule of Impact on Earnings Per Share Calculation (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
For earnings (loss) per share - basic:
Net income (loss) attributable to Iconix Brand Group, Inc.	$ 45,726	$ (35,708)	$ 6,808	$ (16,492)
Accretion of redeemable non-controlling interest	140		(171)
Net income (loss) attributable to Iconix Brand Group, Inc. after the effect of accretion of redeemable non-controlling interest for basic earnings (loss) per share	45,866	(35,708)	6,637	(16,492)
For earnings (loss) per share - diluted:
Net income (loss) attributable to Iconix Brand Group, Inc.	45,726	(35,708)	6,808	(16,492)
Effect of potential conversion of 5.75% Convertible Notes	1,085		5,938
Accretion of redeemable non-controlling interest	140		(171)
Net income (loss) attributable to Iconix Brand Group, Inc. after the effect of potential conversion of 5.75% Convertible Notes for diluted earnings (loss) per share	$ 46,951	$ (35,708)	$ 12,575	$ (16,492)
Basic	$ 3.66	$ (3.07)	$ 0.55	$ (1.62)
Diluted	$ 1.51	$ (3.07)	$ 0.37	$ (1.62)
Weighted average number of common shares outstanding:
Basic	12,517	11,631	12,051	10,169
Diluted	31,189	11,631	33,801	10,169