DEBT OBLIGATIONS (Details)								3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 14, 2015 Extension	Jun. 26, 2015 USD ($)	Apr. 10, 2015 Extension	Feb. 19, 2015 Extension	Oct. 31, 2014 USD ($)	Feb. 11, 2014 USD ($) Extension	Jan. 24, 2013 USD ($) Financing_Counterparty	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) agreement	Sep. 30, 2014 USD ($) agreement	Dec. 31, 2014 USD ($)	Oct. 30, 2014 USD ($)	Apr. 29, 2014 USD ($)	Apr. 28, 2014 USD ($)
FINANCING
Amortization of premiums										$ (678,000)	$ (471,000)
Unamortized debt issuance costs								$ 7,600,000		7,600,000		$ 9,400,000
Restricted equity from payment as dividend								900,300,000		900,300,000
Tuebor
FINANCING
Amount restricted from transfer								414,200,000		414,200,000
Revolving credit facility | One-Month LIBOR
FINANCING
Committed amount on credit agreement						$ 75,000,000
Debt borrowings term						3 years
Number of twelve-month extension maturity periods | Extension						2
Length of extension options						12 months
Basis spread on variable rate (as a percent)						3.50%
Letters of credit
FINANCING
Committed amount on credit agreement						$ 25,000,000
Term master repurchase agreement
FINANCING
Committed amount on master repurchase agreement								300,000,000		$ 300,000,000
Number of extension executed | Extension				1
Committed master repurchase agreements
FINANCING
Number of agreements | agreement										3
Committed amount on master repurchase agreement								1,450,000,000		$ 1,450,000,000		1,150,000,000	$ 450,000,000	$ 450,000,000	$ 300,000,000
Uncommitted securities repurchase facilities | Minimum
FINANCING
Advance rates (as a percent)										65.00%
Uncommitted securities repurchase facilities | Maximum
FINANCING
Advance rates (as a percent)										95.00%
Maturity 30 to 90 Days | Committed master repurchase agreements
FINANCING
Committed amount on master repurchase agreement													$ 650,000,000
Maturing April 10, 2019 | Term master repurchase agreement
FINANCING
Number of extension executed | Extension			1
Maturing on October 30, 2016 | Committed master repurchase agreements
FINANCING
Committed amount on master repurchase agreement								600,000,000		$ 600,000,000		$ 450,000,000
Number of extension executed | Extension	1
Length of extension options										12 months		12 months
Credit Agreement
FINANCING
Committed amount on credit agreement							$ 50,000,000
Number of multiple committed financing counterparties | Financing_Counterparty							1
Credit Agreement | One-Month LIBOR
FINANCING
Basis spread on variable rate (as a percent)							2.75%
Mortgage loan financing
FINANCING
Number of agreements | agreement										36	5
Stated interest rate, minimum (as a percent)										4.25%
Borrowing under credit and security agreement								555,800,000		$ 555,800,000
Stated interest rate, maximum (as a percent)										6.75%
Mortgage loan financing												$ 447,400,000
Net unamortized premiums								7,000,000		$ 7,000,000		5,300,000
Amortization of premiums								200,000	$ 200,000	700,000	$ 500,000
Pledged assets, real estate and lease intangibles, net								$ 723,400,000		$ 723,400,000		$ 591,600,000
Borrowings from the Federal Home Loan Bank | Tuebor
FINANCING
Debt borrowings term										9 years		10 years
Stated interest rate, minimum (as a percent)										0.27%		0.30%
Stated interest rate, maximum (as a percent)										2.74%		2.74%
Weighted average interest rate								0.83%		0.83%		0.79%
Weighted average term										1 year 7 months 13 days		2 years 18 days
Maximum advance limit		$ 2,900,000,000
FHLB borrowings outstanding								$ 1,800,000,000		$ 1,800,000,000		$ 1,600,000,000
Additional committed term financing available from FHLB								462,700,000		$ 462,700,000		$ 289,000,000
Borrowings from the Federal Home Loan Bank | Tuebor | Ladder Capital Corp
FINANCING
Advance rates of total assets (as a percent)		40.00%
Advance rates of total equity (as a percent)		150.00%
Borrowings from the Federal Home Loan Bank | Tuebor | Minimum
FINANCING
Advance rates (as a percent)										50.00%		50.00%
Borrowings from the Federal Home Loan Bank | Tuebor | Maximum
FINANCING
Advance rates (as a percent)										95.20%		95.20%
Borrowings from the Federal Home Loan Bank | Tuebor | CMBS and U.S. Agency Securities
FINANCING
Collateral for debt instrument								1,700,000,000		$ 1,700,000,000		$ 1,600,000,000
Borrowings from the Federal Home Loan Bank | Tuebor | First mortgage commercial real estate loans
FINANCING
Collateral for debt instrument								523,300,000		523,300,000		451,800,000
Credit and Security Agreement
FINANCING
Debt issued					$ 46,750,000
Credit and Security Agreement | One-Month LIBOR
FINANCING
Basis spread on variable rate (as a percent)					1.85%
Credit Agreement and Revolving Credit Facility
FINANCING
Unamortized debt issuance costs								$ 3,700,000		$ 3,700,000		$ 4,000,000