Debt Arrangements - Additional Information (Detail) $ / shares in Units, shares in Millions										1 Months Ended			3 Months Ended		9 Months Ended
		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 ($)	May 23, 2011 USD ($) shares	Apr. 30, 2016 USD ($)	Feb. 28, 2015 USD ($)	Mar. 31, 2013 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) shares	Sep. 30, 2015 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 21, 2013 USD ($)
Debt Instrument [Line Items]
Net proceeds received from issuance of debt															$ 300,000,000
Current portion of long-term debt													$ 76,123,000		76,123,000				$ 61,123,000
Restricted cash													117,806,000		117,806,000				49,544,000
Long term debt	[1]												1,290,064,000		1,290,064,000				1,449,392,000
Debt instrument, cash paid to repurchase convertible notes															178,973,000
Repurchase of equity portion of convertible notes															1,164,000
Non cash additional interest expense on convertible notes															17,789,000	$ 23,408,000
IBG Borrower
Debt Instrument [Line Items]
Termination of license generating with minimum royalty guarantees													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%
Minimum | IBG Borrower
Debt Instrument [Line Items]
Asset coverage ratio, minimum				1.25%
Maximum | IBG Borrower
Debt Instrument [Line Items]
Leverage ratio				4.50%
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]
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											2018-01
Additional interest rate											5.00%
Long term debt													100,000,000		$ 100,000,000				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													767,100,000		$ 767,100,000				812,900,000
Debt Instrument anticipated repayment year and month								2020-01
Debt instrument, Maturity Date								2043-01
Current portion of long-term debt													61,100,000		61,100,000				61,100,000
Restricted cash													54,100,000		54,100,000				48,700,000
Cash interest expense for convertible notes													8,300,000	$ 8,900,000	25,400,000	$ 26,000,000
Long term debt													667,065,000		667,065,000				$ 712,907,000
Convertible Notes | 1.50% Senior Subordinated Notes Due March 15, 2018
Debt Instrument [Line Items]
Principal amount of long term debt					$ 400,000,000								$ 295,100,000		$ 295,100,000
Debt instrument, interest rate, stated percentage					1.50%								1.50%	1.50%	1.50%	1.50%			1.50%
Net proceeds received from issuance of debt					$ 390,600,000
Cash interest expense for convertible notes													$ 1,100,000	$ 1,500,000	$ 4,100,000	$ 4,500,000
Debt instrument, maturity date					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	[2]												274,036,000		$ 274,036,000				$ 357,453,000
Debt instrument, par value of notes repurchased													104,900,000		104,900,000		$ 53,200,000	$ 51,700,000
Debt instrument, cash paid to repurchase convertible notes															36,700,000
Debt instrument, gain (loss) on repurchase of convertible notes													4,200,000		9,600,000
Repurchase of equity portion of convertible notes															1,200,000
Non cash additional interest expense on convertible notes													3,400,000	$ 4,600,000	11,400,000	$ 12,400,000
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							$ 7,000,000		$ 7,000,000				$ 13,000,000
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					30 days
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					5 days
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]
Principal amount of long term debt									$ 300,000,000
Debt instrument, interest rate, stated percentage			2.50%						2.50%				2.50%	2.50%	2.50%	2.50%			2.50%
Net proceeds received from issuance of debt									$ 291,600,000
Cash interest expense for convertible notes													$ 0	$ 1,900,000	$ 3,000,000	$ 5,600,000
Debt instrument, maturity date															Jun. 01, 2016
Long term debt	[3]																		$ 294,048,000
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	3,300,000	4,500,000	9,400,000
Repayment of remaining outstanding balance of convertible notes upon maturity		$ 156,100,000
Convertible Notes | 2.50% Senior Subordinated Notes Due June 2016 | Long | Call Option
Debt Instrument [Line Items]
Convertible notes, common stock option shares | shares									9.8
Payment for the purchased call option									$ 58,700,000
Deferred income tax related to convertible notes									$ 20,600,000				0		0
Senior Secured Term Loan
Debt Instrument [Line Items]
Principal amount of long term debt				$ 300,000,000									292,500,000		292,500,000
Cash interest expense for convertible notes													8,700,000	$ 0	17,000,000	$ 0
Debt instrument, maturity date				Mar. 07, 2021
Long term debt													$ 271,159,000		$ 271,159,000
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%
Senior Secured Term Loan | IBG Borrower
Debt Instrument [Line Items]
Principals of debt amortization terms															Borrowings under the Senior Secured Term Loan amortize yearly at 5% of principal as long as the applicable asset coverage ratio, as defined in the Credit Agreement, remains greater than or equal to 1.65:1.00 as of the end of each fiscal quarter and IBG Borrower timely delivers 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 is 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 will be obligated to pay during the subsequent quarter amortization at 25% per annum, or 15% per annum, respectively. IBG Borrower will also pay amortization at 25% per annum if it fails to timely deliver a compliance certificate to Cortland after each fiscal quarter
Percentage of principal debt amortization on default				25.00%
Senior Secured Term Loan | LIBOR
Debt Instrument [Line Items]
LIBOR floor				1.50%
Senior Secured Term Loan | 1.20:1.00 or greater but less than 1.45:1.00 | IBG Borrower
Debt Instrument [Line Items]
Percentage of principal debt amortization				25.00%
Asset coverage ratio, minimum				1.25%
Asset coverage ratio, maximum				1.45%
Senior Secured Term Loan | 1.45:1.00 or greater but less than 1.65:1.00 | IBG Borrower
Debt Instrument [Line Items]
Percentage of principal debt amortization				15.00%
Asset coverage ratio, minimum				1.45%
Asset coverage ratio, maximum				1.65%

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

[2] During the Current Nine Months, 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. See below for further details.

[3] In April 2016, the Company repurchased $143.9 million par value of the 2.50% Convertible Notes. Upon maturity of the notes on June 1, 2016, the Company repaid the remaining outstanding balance of $156.1 million in cash. See below for further details.