Debt Arrangements - Additional Information (Detail) $ / shares in Units, shares in Millions														1 Months Ended					3 Months Ended		9 Months Ended		12 Months Ended
		Oct. 27, 2017 USD ($)	Aug. 18, 2017 USD ($)	Aug. 02, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 01, 2016 USD ($)	Apr. 04, 2016 USD ($)	Mar. 07, 2016 USD ($)	Mar. 18, 2013 USD ($) d $ / shares shares	Mar. 13, 2013 USD ($) $ / shares shares	Mar. 12, 2013 $ / shares	Nov. 29, 2012 USD ($)	May 23, 2011 USD ($)	Jul. 31, 2017 USD ($)	Jan. 31, 2017 USD ($)	Apr. 30, 2016 USD ($)	Feb. 28, 2015 USD ($)	Mar. 31, 2013 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) shares	Jul. 31, 2019	Mar. 15, 2018 USD ($)	Nov. 24, 2017 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jan. 07, 2016 $ / shares	Jun. 21, 2013 USD ($)
Debt Instrument [Line Items]
Principal amount of long term debt					$ 0
Net proceeds received from issuance of debt																					$ 288,000,000	$ 300,000,000
Loss on extinguishment of debt																			$ 1,539,000	$ (4,186,000)	20,939,000	(8,473,000)
Current portion of long-term debt																			553,549,000		553,549,000		$ 160,435,000
Restricted cash																			279,759,000		279,759,000		177,269,000
Cash interest expense for convertible notes																			0	8,700,000	12,400,000	17,000,000
Long term debt	[1]																		1,013,318,000		1,013,318,000		1,254,160,000
Debt instrument, cash paid to repurchase convertible notes																					58,810,000	178,973,000
Non cash additional interest expense on convertible notes																					13,225,000	17,789,000
Percentage of principal debt quarterly amortization				0.50%
Principal debt quarterly amortization commencement date				Sep. 30, 2017
IBG Borrower
Debt Instrument [Line Items]
Termination of license generating with minimum royalty guarantees				$ 500,000															5,000,000		$ 5,000,000
Equity ownership percentage								35.00%
Premium percentage of aggregate principal amount first two years loan								3.00%
Premium percentage of aggregate principal amount third year loan								3.00%
Premium percentage of aggregate principal amount fourth year loan								1.00%
Ownership by Iconix China								35.00%
Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Principal amount of long term debt		$ 300,000,000
Leverage ratio		4.50%
Cash from escrow deposit returned to Lenders		$ 231,000,000
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
Estimated principal payments																										$ 12,000
Minimum
Debt Instrument [Line Items]
Selling price per share of common stock | $ / shares																													$ 4.53
Minimum | IBG Borrower
Debt Instrument [Line Items]
Asset coverage ratio, minimum				1.25%				1.25%
Maximum
Debt Instrument [Line Items]
Selling price per share of common stock | $ / shares																													$ 59.08
Maximum | IBG Borrower
Debt Instrument [Line Items]
Leverage ratio				4.50%				4.50%
Maximum | Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Leverage ratio		5.75%
Aggregate amount of term loan facility		$ 165,700,000
2012 Senior Secured Notes
Debt Instrument [Line Items]
Principal amount of long term debt												$ 600,000,000
Debt instrument, interest rate, stated percentage												4.229%
Debt instrument, quarterly payment												$ 10,500,000
Debt instrument, frequency of payment																					quarterly
Class A Variable Funding Note
Debt Instrument [Line Items]
Principal amount of long term debt												100,000,000
Variable Funding Notes
Debt Instrument [Line Items]
Principal amount of long term debt																			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%
Debt Instrument anticipated repayment year and month			2020-01														2018-01
Additional interest rate																	5.00%
L/C commitment and the swingline commitment			$ 0
Long term debt	[2]																		90,429,000		$ 90,429,000		100,000,000
2013 Senior Secured Notes
Debt Instrument [Line Items]
Principal amount of long term debt																														$ 275,000,000
Debt instrument, interest rate, stated percentage																														4.352%
Debt instrument, quarterly payment												$ 4,800,000
Debt instrument, frequency of payment																					quarterly
Senior Secured Notes
Debt Instrument [Line Items]
Principal amount of long term debt																			509,300,000		$ 509,300,000		751,800,000
Debt Instrument anticipated repayment year and month												2020-01
Debt instrument, Maturity Date												2043-01
Loss on extinguishment of debt														$ 2,300,000
Current portion of long-term debt																			42,700,000		42,700,000		95,300,000
Restricted cash																			38,700,000		38,700,000		112,400,000
Mandatory principal prepayment														152,200,000
Debt issue discount costs														2,000,000
Prepayment penalty														300,000
Cash interest expense for convertible notes																			7,400,000	$ 8,300,000	23,000,000	$ 25,400,000
Long term debt																			418,847,000		418,847,000		651,784,000
Senior Secured Term Loan
Debt Instrument [Line Items]
Principal amount of long term debt					0			$ 300,000,000
Debt instrument, annual principal prepayment															$ 36,700,000								28,700,000
Deferred financing costs															1,000,000				$ 800,000		800,000		1,000,000
Loss on extinguishment of debt															500,000						5,000,000		7,400,000
Mandatory principal prepayment															23,500,000
Debt issue discount costs																					$ 1,700,000		2,100,000
Maturity date of credit agreement								Mar. 07, 2021
Long term debt	[3]																						244,906,000
Margin applied to LIBOR								10.00%
Net proceeds received from issuance of debt							$ 264,200,000
Percentage of principal debt amortization								5.00%
Asset coverage ratio, minimum								165.00%
Interest rate increase additional per annum								3.00%
Payment of unpaid principal and accrued interest of lenders								50.00%
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
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
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
Senior Secured Term Loan | Accounts Payable And Accrued Liabilities
Debt Instrument [Line Items]
Accrued Expenses																							$ 6,800,000
Senior Secured Term Loan | IBG Borrower
Debt Instrument [Line Items]
Percentage of principal debt amortization								25.00%
Asset coverage ratio, minimum								1.25%
Principals of debt amortization terms																					Borrowings under the Senior Secured Term Loan amortized yearly at 5% of principal as long as the applicable asset coverage ratio, as defined in the Credit Agreement, remained greater than or equal to 1.65:1.00 as of the end of each fiscal quarter and IBG Borrower timely delivered a compliance certificate to Cortland after each fiscal quarter. If IBG Borrower’s asset coverage ratio measured as of the end of a certain fiscal quarter was 1.25:1.00 or greater but less than 1.45:1.00, or 1.45:1.00 or greater but less than 1.65:1.00, IBG Borrower was obligated to pay during the subsequent quarter amortization at 25% per annum, or 15% per annum, respectively. IBG Borrower would also pay amortization at 25% per annum if it failed to timely deliver a compliance certificate to Cortland after each fiscal quarter.
Asset coverage ratio, maximum - Range one								1.45%
Asset coverage ratio, minimum - Range two								1.45%
Asset coverage ratio, maximum - Range two								1.65%
Percentage of principal debt amortization - Range two								15.00%
Percentage of principal debt amortization on default								25.00%
Senior Secured Term Loan | LIBOR
Debt Instrument [Line Items]
LIBOR floor								1.50%
2012 Senior Secured Notes
Debt Instrument [Line Items]
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]
Debt instrument, quarterly principal payments															$ 4,500,000
Debt instrument, decrease in quarterly principal payments														$ 3,400,000
Convertible Notes | Deutsche Bank AG
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage																			1.50%		1.50%
Payment from Escrow Account to acquire convertible notes																					$ 59,200,000
Convertible Notes | Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Cash from escrow deposit returned to Lenders		231,000,000
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Principal amount of long term debt									$ 400,000,000				$ 300,000,000						$ 236,200,000		$ 236,200,000
Debt instrument, interest rate, stated percentage									1.50%				2.50%						1.50%	1.50%	1.50%	1.50%	1.50%
Net proceeds received from issuance of debt									$ 390,600,000				$ 291,600,000
Debt instrument, Maturity Date																			2018-03
Cash interest expense for convertible notes																			$ 1,100,000	$ 1,100,000	$ 3,300,000	$ 4,100,000
Maturity date of credit agreement									Mar. 15, 2018
Debt instrument, payment terms																					The 1.50% Convertible Notes bear interest at an annual rate of 1.50%, payable semi-annually in arrears on March 15 and September 15 of each year, beginning on September 15, 2013
Debt instrument, effective interest rate									6.50%
Debt instrument, conversion rate									32.4052
Principal amount of each convertible note									$ 1,000
Convertible notes, initial conversion price per share | $ / shares									$ 30.86
Long term debt	[4]																		230,929,000		$ 230,929,000		$ 277,518,000
Debt instrument, par value of notes repurchased																			58,900,000		58,900,000		104,900,000				$ 53,200,000	$ 51,700,000
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
Non cash additional interest expense on convertible notes																			3,300,000	3,400,000	10,100,000	11,400,000
Sold warrants, shares of common stock | shares										13.0
Sold warrants, shares of common stock strike price per share | $ / shares										$ 35.5173
Sold warrants, shares of common stock exercise date										Jun. 18, 2018
Sold warrants, shares of common stock expiring date										Sep. 01, 2018
Proceeds received from sale of sold warrants										$ 57,700,000
Adjustments to additional paid in capital due convertible note hedge and warrants																		$ 3,000,000
Convertible notes, warrant strike price | $ / shares											$ 35.5173
Percentage of premiums											52.50%
Selling price per share of common stock | $ / shares											$ 23.29
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Long | Call Option
Debt Instrument [Line Items]
Convertible notes, common stock option shares | shares									13.0
Payment for the purchased call option										84,100,000
Deferred income tax related to convertible notes										$ 29,400,000									$ 1,800,000		$ 1,800,000		$ 5,600,000
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Deutsche Bank AG
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage																			1.50%		1.50%
Proceeds from deposits in escrow account to repay																					$ 240,000,000
Proceeds from initial escrow funds to repurchase outstanding debt																					59,000,000
Additional amount held in escrow																			$ 300,000,000		300,000,000
Line of credit remaining outstanding principal amount																			236,000,000		$ 236,000,000
Payment from Escrow Account to acquire convertible notes																			59,200,000
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																							7.4
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Scenario 1
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days | d									20
Debt instrument, convertible, threshold consecutive trading days | d									30
Debt instrument, redemption price, percentage																					100.00%
Debt instrument, redemption, description																					price equal to 100% of the principal amount of the 1.50% Convertible Notes, plus accrued and unpaid interest, if any
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Scenario 2
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days | d									5
Debt instrument, convertible, threshold consecutive trading days | d									5
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Minimum
Debt Instrument [Line Items]
Percentage of closing price to trigger debt conversion									130.00%
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018 | Maximum
Debt Instrument [Line Items]
Percentage of closing price to trigger debt conversion									98.00%
Convertible Notes | 2.50% Senior Subordinated Notes Due June 2016
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage							2.50%
Cash interest expense for convertible notes																			0	0	$ 0	3,000,000
Debt instrument, par value of notes repurchased																$ 143,900,000
Debt instrument, cash paid to repurchase convertible notes																$ 145,600,000
Debt instrument, gain (loss) on repurchase of convertible notes																						(1,200,000)
Non cash additional interest expense on convertible notes																			0	0	0	4,500,000
Repayment of remaining outstanding balance of convertible notes upon maturity						$ 156,100,000
2017 Senior Secured Term Loan Due 2022
Debt Instrument [Line Items]
Principal amount of long term debt				$ 300,000,000															298,500,000		298,500,000
Cash interest expense for convertible notes																			4,000,000	$ 0	4,000,000	$ 0
Maturity date of credit agreement				Aug. 02, 2022
Long term debt	[5]																		$ 286,823,000		$ 286,823,000
Margin applied to LIBOR				7.00%
Interest rate increase additional per annum				3.00%
Payment of unpaid principal and accrued interest of lenders				50.00%
2017 Senior Secured Term Loan Due 2022 | IBG Borrower
Debt Instrument [Line Items]
Equity ownership percentage				35.00%
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%
First Delayed Draw Term Loan | Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Aggregate amount of term loan facility		25,000,000
Second Delayed Draw Term Loan | Scenario, Forecast | Deutsche Bank AG
Debt Instrument [Line Items]
Aggregate amount of term loan facility																									$ 140,700,000
Senior Secured Term Loan Due 2022 | Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Principal amount of long term debt		$ 300,000,000
Leverage ratio		4.75%
Aggregate amount of term loan facility		$ 225,000,000
Amortization rate per annum		2.00%
Senior Secured Term Loan Due 2022 | Minimum | Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Amortization rate per annum		2.00%
Senior Secured Term Loan Due 2022 | Maximum | Scenario, Forecast | Deutsche Bank AG | Subsequent Event
Debt Instrument [Line Items]
Amortization rate per annum																								10.00%
Second Delayed Draw Term Loan | Minimum | Deutsche Bank AG | Subsequent Event
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

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

[2] On August 18, 2017, the Company entered into an amendment of its Variable Funding Note which extended the anticipated repayment date for the Variable Funding Notes from January 2018 to January 2020. See below for further details.

[3] On June 30, 2017, the Company repaid the remaining outstanding principal balance of the Senior Secured Term Loan and accordingly, the Company wrote off the remaining portion of the deferred financing costs and original issue discount associated with the debt facility. See below for further details.

[4] During FY 2016, the Company repurchased a total of $104.9 million par value (of which $51.7 million and $53.2 million were purchased in June 2016 and July 2016, respectively) of the 1.50% Convertible Notes. During the Current Quarter, the Company repurchased a total of $58.9 million par value of the 1.50% Convertible Notes. See below for further details.

[5] On August 2, 2017, the Company entered into a long-term refinancing arrangement with Deutsche Bank AG for an aggregate principal amount of $300 million. See below for further details.