Debt Arrangements - Additional Information (Detail)															1 Months Ended								3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
		Mar. 15, 2018 USD ($)	Mar. 14, 2018 USD ($)	Feb. 22, 2018 USD ($) d	Dec. 07, 2017 USD ($)	Nov. 02, 2017 USD ($)	Oct. 27, 2017 USD ($)	Aug. 18, 2017 USD ($)	Aug. 02, 2017 USD ($)	Jun. 30, 2017 USD ($)	Apr. 04, 2016 USD ($)	Mar. 07, 2016 USD ($)	Mar. 18, 2013 USD ($)	Nov. 29, 2012 USD ($)	Jun. 30, 2018 USD ($) shares	Apr. 30, 2018 USD ($) shares	Mar. 16, 2018 USD ($) shares	Jul. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 28, 2015 USD ($)	Jul. 31, 2014 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) shares	Jul. 31, 2019	Oct. 01, 2018	Jul. 01, 2018	Feb. 12, 2018 USD ($)	Nov. 24, 2017 USD ($)	Oct. 26, 2017 USD ($)	Jun. 21, 2013 USD ($)
Debt Instrument [Line Items]
Principal amount of long term debt							$ 240,700,000			$ 0
Net proceeds received from issuance of debt																										$ 95,700,000	$ 288,000,000
Debt service coverage ratio															145.00%								135.00%			135.00%						145.00%
Percentage of residual royalty collections required to allocate																															50.00%	25.00%
Payments of securitized financing transaction																										$ 5,423,000	7,145,000
Payment for the acquisition of Brand																										284,000	109,000
Payment of long-term debt																										145,655,000	583,157,000
Deferred financing costs							5,400,000																					$ 200,000
Gain (loss) on extinguishment of debt																								$ (1,539,000)		4,473,000	(20,939,000)
Debt issue discount costs							$ 9,300,000
Current portion of long-term debt																							$ 50,406,000			50,406,000		44,349,000
Restricted cash																							21,174,000			21,174,000		48,766,000
Cash interest expense for convertible notes																							$ 0			$ 0	12,400,000
Leverage ratio							450.00%
Debt instrument, interest rate, stated percentage																							5.75%			5.75%
Net proceeds from Permitted Capital Raising Transactions							$ 100,000,000
Financial covenant compliance on a pro forma basis																										The Company raising additional funds through various sources (and/or achieving a reduction in the outstanding principal amount of the 2018 Notes) in an aggregate amount of at least $100 million which will be utilized to repay the 2018 Notes and provide at least $25 million of additional cash to enhance liquidity and be used for general corporate purposes, (ii) the Company being in financial covenant compliance, on a pro forma basis as of the time of the requested borrowing and on a projected basis for the succeeding 12 months
Projected Succeding period of borrowings							12 months
Repayment of remaining outstanding principal balance					$ 5,000,000		$ 231,000,000
Non cash additional interest expense on convertible notes																										$ 7,574,000	13,225,000
Long term debt, fair value																							$ 55,878,000			55,878,000		0
Principal outstanding balance	[1]																						$ 691,638,000			$ 691,638,000		800,842,000
Debt instrument, cash paid to repurchase convertible notes																											58,810,000
1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage																							1.50%			1.50%
Repurchase of equity portion of convertible notes																										$ 23,250,000
5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage																							5.75%			5.75%
5.75% Senior Subordinated Notes Due August 2023 | Common Stock
Debt Instrument [Line Items]
Shares issued on conversion of 5.75% Convertible Notes (in shares) | shares																										11,035,000
Maximum
Debt Instrument [Line Items]
Leverage ratio							575.00%
Aggregate amount of term loan facility							$ 165,700,000
MG Icon
Debt Instrument [Line Items]
Ownership by Iconix China														50.00%
Hardy Way, LLC
Debt Instrument [Line Items]
Joint venture ownership percentage														85.00%
Zoo York brand
Debt Instrument [Line Items]
Ownership Percentage														100.00%
IBG Borrower
Debt Instrument [Line Items]
Termination of license generating with minimum royalty guarantees									$ 500,000
IBG Borrower | Minimum
Debt Instrument [Line Items]
Asset coverage ratio, minimum									125.00%
IBG Borrower | Maximum
Debt Instrument [Line Items]
Leverage ratio									450.00%
2012 Senior Secured Notes
Debt Instrument [Line Items]
Principal amount of long term debt														$ 600,000,000
Debt instrument, quarterly payment														10,500,000
Debt instrument, frequency of payment																										quarterly
Proceeds from issuance of debt instrument														150,400,000
Payments of securitized financing transaction														20,900,000
2012 Senior Secured Notes | Umbro
Debt Instrument [Line Items]
Payment for the acquisition of Brand														218,300,000
Variable Funding Notes
Debt Instrument [Line Items]
Principal amount of long term debt														100,000,000									$ 100,000,000			$ 100,000,000
Net proceeds received from issuance of debt																					$ 100,000,000
Commitment fee on the unused portion of the variable funding notes facility																					0.50%
Additional interest rate																					5.00%
Debt Instrument anticipated repayment year and month								2020-01
L/C commitment and the swingline commitment								$ 0
2013 Senior Secured Notes
Debt Instrument [Line Items]
Principal amount of long term debt																																				$ 275,000,000
Debt instrument, quarterly payment														4,800,000
Debt instrument, frequency of payment																										quarterly
Payments of securitized financing transaction														$ 7,200,000
Senior Secured Notes
Debt Instrument [Line Items]
Principal amount of long term debt																							476,200,000			$ 476,200,000		508,200,000
Additional interest rate														5.00%
Debt Instrument anticipated repayment year and month														2020-01
Debt instrument, Maturity Date														2043-01
Debt instrument description of interest																										If the Co-Issuers have not repaid or refinanced the Senior Secured Notes prior to the anticipated repayment date, additional interest will accrue on the Senior Secured Notes at a rate equal to the greater of (A) 5% per annum and (B) a per annum interest rate equal to the excess, if any, by which the sum of (i) the yield to maturity (adjusted to a quarterly bond-equivalent basis), on the anticipated repayment date of the United States treasury security having a term closest to 10 years plus (ii) 5% plus (iii) with respect to the 2012 Senior Secured Notes, 3.4%, or with respect to the 2013 Senior Secured Notes, 3.14%, exceeds the original interest rate.
Anticipated repayment date														10 years
Payment of long-term debt																						$ 1,600,000
Debt instrument, annual principal prepayment																			$ 36,700,000
Deferred financing costs																			500,000
Gain (loss) on extinguishment of debt																		$ (2,300,000)	(500,000)
Debt instrument, quarterly principal payments																			4,500,000
Mandatory principal prepayment																		152,200,000
Debt issue discount costs																		2,000,000
Prepayment penalty																		300,000
Current portion of long-term debt																							42,700,000			$ 42,700,000		42,700,000
Restricted cash																							20,300,000			20,300,000		29,900,000
Cash interest expense for convertible notes																							5,600,000	6,200,000		16,800,000	21,300,000
2012 Senior Secured Notes
Debt Instrument [Line Items]
Excess interest rate on original interest rate														3.40%
Debt instrument, quarterly principal payments																			9,900,000
Debt instrument, decrease in quarterly principal payments																		7,300,000
2013 Senior Secured Notes
Debt Instrument [Line Items]
Excess interest rate on original interest rate														3.14%
Debt instrument, decrease in quarterly principal payments																		$ 3,400,000
Senior Secured Term Loan
Debt Instrument [Line Items]
Principal amount of long term debt							57,800,000		$ 300,000,000														190,400,000			190,400,000									$ 300,000,000
Deferred financing costs							800,000
Gain (loss) on extinguishment of debt							8,800,000
Debt issue discount costs																										19,500,000		8,000,000
Current portion of long-term debt																							7,700,000			7,700,000		1,700,000
Cash interest expense for convertible notes																							4,500,000	4,000,000		12,500,000	4,000,000
Maturity date of credit agreement									Aug. 02, 2022
Margin applied to LIBOR									7.00%
Percentage of principal debt quarterly amortization									0.50%
Principal debt quarterly amortization commencement date									Sep. 30, 2017
Estimated principal payments																																		$ 12,000,000
Repayment of remaining outstanding principal balance																										5,000,000
Interest rate increase additional per annum									3.00%
Payment of unpaid principal and accrued interest of lenders									50.00%
Principal amount of long term debt																							170,900,000			170,900,000		$ 74,800,000
Commitment fee amount																										1,200,000
Non cash additional interest expense on convertible notes																							$ 1,300,000	500,000		$ 3,000,000	500,000
Senior Secured Term Loan | IBG Borrower
Debt Instrument [Line Items]
Ownership by Iconix China									35.00%
Premium percentage of aggregate principal amount first year loan									5.00%
Premium percentage of aggregate principal amount second year loan									3.00%
Convertible Notes
Debt Instrument [Line Items]
Cash from escrow deposit returned to lenders							231,000,000
Payment from Escrow Account to acquire convertible notes																											59,200,000
Debt instrument, interest rate, stated percentage																							1.50%			1.50%
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Principal amount of long term debt				$ 125,000,000									$ 400,000,000
Net proceeds received from issuance of debt													$ 390,600,000
Cash interest expense for convertible notes																							$ 0	$ 1,100,000		$ 600,000	$ 3,300,000
Maturity date of credit agreement				Mar. 15, 2018
Debt instrument, interest rate, stated percentage				1.50%									1.50%							1.50%			1.50%	1.50%	1.50%	1.50%	1.50%	1.50%	1.50%
Repayment of remaining outstanding principal balance		$ 111,200,000
Non cash additional interest expense on convertible notes																							$ 0	$ 3,500,000		$ 1,900,000	$ 10,800,000
Debt instrument, par value of notes repurchased																				$ 104,900,000								$ 58,900,000	$ 104,900,000
Debt instrument, cash paid to repurchase convertible notes																												59,300,000	36,700,000
Debt instrument, gain (loss) on repurchase of convertible notes																												(1,500,000)	9,600,000
Repurchase of equity portion of convertible notes																													$ 1,200,000
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Common Stock
Debt Instrument [Line Items]
Debt instrument, shares issued to repurchase convertible notes | shares																													7,400,000
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Principal amount of long term debt				$ 125,000,000																			111,000,000			111,000,000
Cash interest expense for convertible notes																							$ 1,600,000	$ 0	$ 0	$ 3,900,000
Debt instrument, interest rate, stated percentage				5.75%																			5.75%	5.75%	5.75%	5.75%	5.75%
Reduction in outstanding principal amount															$ 4,200,000	$ 4,200,000	$ 9,600,000
Debt instrument convertible conversion price as percentage upon automatic conversion				5.75%
Debt instrument convertible conversion price as percentage upon mandatory conversion				5.75%
Debt instrument, convertible, threshold trading days | d				10
Volume weighted average price description																										If the Company elects to pay all or a portion of a Conversion Make-Whole Payment in shares of common stock, the number of shares of common stock payable will be equal to the applicable Conversion Make-Whole Payment divided by the average of the 10 individual volume-weighted average prices for the 10-trading day period immediately preceding the applicable conversion date.
Debt instrument, convertible, threshold consecutive trading days | d				30
Debt instrument, redemption price, percentage				100.00%
Debt instrument, redemption, description																										Each holder will have the right, at its option, to require the Company to repurchase for cash all or a portion of such holder’s 5.75% Convertible Notes at a fundamental change purchase price equal to 100% of the principal amount of the 5.75% Convertible Notes to be repurchased, together with interest accrued and unpaid to, but excluding, the fundamental change purchase date.
Debt instrument, restrictive covenants																										The Company is subject to certain restrictive covenants pursuant to the 5.75% Convertible Note Indenture, including limitations on (i) liens, (ii) indebtedness, (iii) asset sales, (iv) restricted payments and investments, (v) prepayments of indebtedness and (vi) transactions with affiliates.
Debt conversion original debt amount																	$ 8,800,000
Shares issued on conversion of 5.75% Convertible Notes (in shares) | shares															2,700,000	2,700,000	4,500,000
Stock issued pursuant to conversion settlement | shares															2,000,000	2,000,000	1,900,000
Long term debt, fair value																							$ 55,900,000			$ 55,900,000
Principal outstanding balance																							111,000,000			$ 111,000,000
Stock issued during period for payment of interest | shares																										6,300,000
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023 | Fair Value Option
Debt Instrument [Line Items]
Long term debt, fair value																							$ 55,900,000			$ 55,900,000
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023 | Common Stock
Debt Instrument [Line Items]
Debt conversion original debt amount															$ 5,200,000	$ 5,200,000
Convertible Notes | 5.75% Senior Subordinated Notes Due August 2023 | Other Income
Debt Instrument [Line Items]
Gain on conversion of debt															$ 200,000	$ 200,000	$ 800,000
Convertible Notes | 2.50% Senior Subordinated Notes Due June 2016
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage											2.50%
Convertible Notes | Minimum | 1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Reduction in outstanding principal amount				$ 100,000,000
First Delayed Draw Term Loan
Debt Instrument [Line Items]
Debt issue discount costs						$ 1,000,000
Aggregate amount of term loan facility						25,000,000	$ 25,000,000
Aggregate amount of term loan received in cash						$ 24,000,000
Second Delayed Draw Term Loan
Debt Instrument [Line Items]
Aggregate amount of term loan facility			$ 140,700,000
Aggregate amount of term loan received in cash			110,000,000
Second Delayed Draw Term Loan | 1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Aggregate amount of term loan facility			$ 110,000,000
Senior Secured Term Loan Due 2022 | Minimum
Debt Instrument [Line Items]
Amortization rate per annum							2.00%
Senior Secured Term Loan Due 2022 | Maximum | Scenario, Forecast
Debt Instrument [Line Items]
Amortization rate per annum																														10.00%
Second Delayed Draw Term Loan | Minimum
Debt Instrument [Line Items]
Additional funds to be raised through various sources							$ 100,000,000
Additional funds to enhance liquidity for general corporate purpose							$ 25,000,000
5.75% Senior Subordinated Notes Due August 2023
Debt Instrument [Line Items]
Estimated principal payments																																	$ 6,100,000
5.75% Senior Subordinated Notes Due August 2023 | Maximum
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage																																	5.75%
2016 Senior Secured Term Loan
Debt Instrument [Line Items]
Principal amount of long term debt										0		$ 300,000,000
Debt instrument, annual principal prepayment																				28,700,000									$ 28,700,000
Deferred financing costs																				1,000,000								800,000	1,000,000
Gain (loss) on extinguishment of debt																												(5,000,000)	(7,400,000)
Mandatory principal prepayment																			23,500,000
Debt issue discount costs																				2,100,000								$ 1,700,000
Maturity date of credit agreement												Mar. 07, 2021
Margin applied to LIBOR												10.00%
Net proceeds received from issuance of debt											$ 264,200,000
Premium prepayment of aggregate principal amount																				4,300,000
Voluntary prepayment amount																			23,000,000
Voluntary prepayment premium																			3,400,000
Additional mandatory prepayment premium																			$ 3,400,000
2016 Senior Secured Term Loan | Discontinued Operations | Entertainment
Debt Instrument [Line Items]
Debt instrument, annual principal prepayment										140,000,000
Deferred financing costs										4,700,000
Debt issue discount costs										9,400,000
Premium prepayment of aggregate principal amount										15,200,000
2016 Senior Secured Term Loan | Continuing Operations
Debt Instrument [Line Items]
Deferred financing costs										2,300,000
Debt issue discount costs										4,400,000
Voluntary prepayment amount										66,000,000
Voluntary prepayment premium										$ 7,200,000
2016 Senior Secured Term Loan | Accounts Payable And Accrued Liabilities
Debt Instrument [Line Items]
Accrued Expenses																				$ 6,800,000									$ 6,800,000
2016 Senior Secured Term Loan | LIBOR
Debt Instrument [Line Items]
LIBOR floor												1.50%

[1] Carrying amounts include aggregate unamortized debt discount and debt issuance costs.