SUBSEQUENT EVENTS - Additional Information (Details) - $ / shares		3 Months Ended	6 Months Ended	12 Months Ended
	Jul. 25, 2021	Mar. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Subsequent Event [Line Items]
Common stock, par value (in dollars per share)			$ 0.01	$ 0.01
Preferred stock, par value (in dollars per share)			$ 0.10	$ 0.10
Cumulative Redeemable Preferred Stock, Series E [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate		7.50%	7.50%	7.50%
Subsequent Event [Member] | Benefit Street Partners Realty Trust, Inc. [Member] | Merger Agreement [Member]
Subsequent Event [Line Items]
Merger agreement date	Jul. 25, 2021
Merger agreement completion period, description	The Merger is expected to be completed in the fourth quarter of 2021.
Subsequent Event [Member] | Benefit Street Partners Realty Trust, Inc. [Member] | Merger Agreement [Member] | Cumulative Redeemable Preferred Stock, Series E [Member]
Subsequent Event [Line Items]
Preferred stock, dividend rate	7.50%
Preferred stock, par value (in dollars per share)	$ 0.10
Convertible preferred stock, shares issued upon conversion	1
Convertible preferred stock, par value per share	$ 0.01
Convertible preferred stock, terms of conversion	In addition, each outstanding share of the Company’s 7.50% Series E Cumulative Redeemable Preferred Stock, $0.10 par value per share, will be converted into the right to receive one newly-issued 7.50% Series E Cumulative Redeemable Preferred Share, $0.01 par value per share, of BSPRT (the “BSPRT Series E Preferred Stock”). Cash will be paid in lieu of any fractional shares of BSPRT Common Stock that would otherwise have been received as a result of the Merger
Subsequent Event [Member] | Benefit Street Partners Realty Trust, Inc. [Member] | Merger Agreement [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Common stock, par value (in dollars per share)	$ 0.01
Sale of stock, description of transaction	Under the terms of the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each issued and outstanding share of the Company’s common stock will be converted into the right to receive: from BSPRT, (A) a number of shares of BSPRT’s common stock, $0.01 par value per share (which will be renamed Class A common stock) (“BSPRT Common Stock”) equal to the quotient (rounded to the nearest one ten-thousandth) determined by dividing (i) the Company’s adjusted book value per share by (ii) BSPRT’s adjusted book value per share (the “Per Share Stock Consideration”), and (B) a cash amount equal to the product of (rounding to the nearest cent) (x) the Company’s adjusted book value per share multiplied by 15.75%, multiplied by (y) 22.5%, without any interest thereon (the “Per Share Cash Consideration” and together with the Per Share Stock Consideration, the “Per Common Share BSPRT Consideration”); and from the Parent Manager, a cash amount equal to the product of (rounding to the nearest cent) (A) the Company’s adjusted book value per share multiplied by 15.75%, multiplied by (B) 77.5%, without any interest thereon (together with the Per Common Share BSPRT Consideration, the “Total Per Common Share Consideration”).
Percentage of book value adjustments in per share of stock consideration	15.75%
Percentage of per share cash consideration	22.50%
Percentage of total per common share consideration	77.50%