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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
For earnings (loss) per share - basic:
Net income (loss) from continuing operations attributable to Iconix Brand Group, Inc.	$ 20,224	$ (550,571)	$ (31,446)	$ (559,707)
Accretion of redeemable non-controlling interest	(5,744)	(547)	(8,652)	(1,641)
Net income (loss) attributable to Iconix Brand Group, Inc. after accretion of redeemable non- controlling interest for basic earnings (loss) per share	14,480	(551,118)	(40,098)	(561,348)
Net income (loss) from discontinued operations attributable to Iconix Brand Group, Inc.		(2,130)		46,369
Net income (loss) attributable to Iconix Brand Group, Inc. for basic earnings (loss) per share	$ 14,480	$ (553,248)	$ (40,098)	$ (514,979)
Continuing operations	$ 0.20	$ (9.64)	$ (0.62)	$ (9.83)
Discontinued operations		(0.04)		0.81
Earnings (loss) per share - basic	$ 0.20	$ (9.67)	$ (0.62)	$ (9.02)
For earnings (loss) per share - diluted:
Net income (loss) from continuing operations attributable to Iconix Brand Group, Inc.	$ 20,224	$ (550,571)	$ (31,446)	$ (559,707)
Effect of potential conversion of 5.75% Convertible Notes	(15,641)		(59,066)
Accretion of redeemable non-controlling interest	(5,744)	(547)	(8,652)	(1,641)
Net loss attributable to Iconix Brand Group, Inc. after the effect of potential conversion of 5.75% Convertible Notes and accretion of redeemable non- controlling interest for diluted earnings (loss) per share	(1,161)	(551,118)	(99,164)	(561,348)
Net income (loss) from discontinued operations attributable to Iconix Brand Group, Inc.		(2,130)		46,369
Net loss attributable to Iconix Brand Group, Inc. for diluted earnings (loss) per share	$ (1,161)	$ (553,248)	$ (99,164)	$ (514,979)
Continuing operations	$ (0.01)	$ (9.64)	$ (0.81)	$ (9.83)
Discontinued operations		(0.04)		0.81
Earnings (loss) per share - diluted	$ (0.01)	$ (9.67)	$ (0.81)	$ (9.02)
Weighted average number of common shares outstanding:
Basic	71,844	57,189	64,577	57,081
Diluted	175,910	57,189	123,096	57,081