INVESTMENT IN UNCONSOLIDATED JOINT VENTURES - Additional Information (Details)			1 Months Ended	3 Months Ended		12 Months Ended
		Apr. 15, 2016 USD ($)	Apr. 30, 2012	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 08, 2019 USD ($)	Aug. 07, 2015 USD ($)	Mar. 22, 2013	Apr. 15, 2011
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures	[1]					$ 40,354,000	$ 35,441,000
Distributions from operations of investment in unconsolidated joint ventures						1,250,000	0	$ 1,017,000
Expenses from investment						(13,381,000)	(15,291,000)	$ (15,861,000)
Ladder Capital Realty Income Partnership I LP
Schedule of Equity Method Investments [Line Items]
Minimum Average Net Equity Partnership Investment as Basis for Management Fee Reduction		$ 100,000,000
Sales Commissions and Fees					$ 6,900		0
Ladder Capital Realty Income Partnership I LP | LP Units
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)												10.00%
Grace Lake JV, LLC
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures						$ 5,316,000	4,908,000
Percentage of equity kicker received with right to convert upon capital event			25.00%
Preferred return used to determine distribution of excess cash flow (as a percent)						8.25%
Percentage of distribution of all excess cash flows and all disposition proceeds upon any sale entitled after consideration of preferred return and return of equity remaining in the property to operating partner						25.00%
Percentage of investment of operating partner						81.00%
Grace Lake JV, LLC | LP Units
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)											19.00%
Grace Lake JV, LLC | Limited liability company
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)						19.00%
24 Second Avenue Holdings LLC
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures						$ 35,038,000	30,533,000
Ownership interest (as a percent)										73.80%
Amount contributed										$ 31,100,000
Profit multiplier ratio										1.70
Ownership percentage after achievement of profit multiplier ratio										50.00%
Expenses from investment				$ (1,100,000)	(1,400,000)	(900,000)
Interest costs capitalized				$ 1,300,000	900,000	1,500,000
24 Second Avenue Holdings LLC | Operating Partner
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)										26.20%
Ownership percentage after achievement of profit multiplier ratio										50.00%
24 Second Avenue Holdings LLC | Co-venturer
Schedule of Equity Method Investments [Line Items]
Loans payable outstanding from unconsolidated joint venture						46,700,000	$ 36,500,000
24 Second Avenue Holdings LLC | Co-venturer | Construction Loan
Schedule of Equity Method Investments [Line Items]
Committed amount on credit agreement						50,465,000
Outstanding amount under credit agreement						46,700,000
Remaining capital commitment to operating partner						$ 600,000
Apartment Building | 24 Second Avenue Holdings LLC
Schedule of Equity Method Investments [Line Items]
Number of real estate properties | property						31
Number of real estate properties, under contract | property						16
Real estate properties, under contract						$ 39,500,000
Real estate properties, under contract, deposit						10.00%
Other | 24 Second Avenue Holdings LLC
Schedule of Equity Method Investments [Line Items]
Number of real estate properties | property						1
Consolidated Joint Ventures | Out-of-Period Adjustment Related to Prior Years
Schedule of Equity Method Investments [Line Items]
Distributions from operations of investment in unconsolidated joint ventures					$ 900,000
Subsequent Event | 24 Second Avenue Holdings LLC | First mortgage loan
Schedule of Equity Method Investments [Line Items]
Committed amount on credit agreement									$ 50,500,000
Subsequent Event | 24 Second Avenue Holdings LLC | Mezzanine Loan
Schedule of Equity Method Investments [Line Items]
Committed amount on credit agreement									$ 6,500,000

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.