Schedule of Impact on Earnings Per Share Calculation (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
For earnings (loss) per share - basic:
Net income (loss) attributable to Iconix Brand Group, Inc.	$ 4,188	$ (21,826)
Accretion of redeemable non-controlling interest		(394)
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	4,188	(22,220)
For earnings (loss) per share - diluted:
Net income (loss) attributable to Iconix Brand Group, Inc.	4,188	(21,826)
Effect of potential conversion of 5.75% Convertible Notes	4,078
Accretion of redeemable non-controlling interest		(394)
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	$ 8,266	$ (22,220)
Basic	$ 0.30	$ (1.89)	$ 0.41
Diluted	$ 0.26	$ (1.89)	$ 0.32
Weighted average number of common shares outstanding:
Basic	13,805	11,772
Diluted	31,628	11,772