SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Redeemable Common Stock) (Details) - USD ($)					12 Months Ended				121 Months Ended
	Mar. 20, 2019	Jun. 01, 2018	Apr. 23, 2018	Dec. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Summary of Significant Accounting Policies [Line Items]
Share holding term						1 year
Maximum percentage of weighted-average shares outstanding available for redemption during any calendar year						5.00%
Share redemption program, termination period				10 days		10 days
Maximum number of shares redeemable per quarter, value						$ 3,000,000.0
Redemption price percentage of most recent estimated value per share				95.00%
Proceeds from issuance of common stock, dividend reinvestment plan						800,000
Shares of common stock sold under dividend reinvestment plan									$ 76,300,000
Redemptions of common stock	$ 8,600,000					10,028,000	$ 123,613,000	$ 74,780,000	285,400,000
Other liabilities						19,801,000	21,006,000		19,801,000
Common Stock
Summary of Significant Accounting Policies [Line Items]
Redemptions of common stock						$ 10,000	113,000	$ 53,000
Maximum | Subsequent Event
Summary of Significant Accounting Policies [Line Items]
Shares of common stock sold under dividend reinvestment plan					$ 800,000
Self-tender Offer (SOR Offer)
Summary of Significant Accounting Policies [Line Items]
Number of shares authorized to be repurchased (in shares)			8,234,217
Average cost per share (in USD per share)			$ 10.93			$ 9.41
Authorized amount			$ 90,000,000.0
Treasury stock, acquired (in shares)		9,527,724	1,294,910
Treasury stock, acquired		$ 104,100,000	$ 14,100,000
Stock repurchased during period (in shares)						3,057
Stock repurchased during period						$ 29,000
Unfulfilled Redemption Request
Summary of Significant Accounting Policies [Line Items]
Other liabilities						800,000	$ 10,000,000.0		$ 800,000
Share Redemption Program | Common Stock
Summary of Significant Accounting Policies [Line Items]
Redemptions of common stock						$ 10,000,000.0
Number of shares non-redeemable do to limitation, shares						5,813,699
Number of shares non-redeemable do to limitation, value						$ 58,700,000
After 2019
Summary of Significant Accounting Policies [Line Items]
Share redemption program, termination period						10 days
Maximum number of shares redeemable per year, value						$ 1,000,000.0
Funds available for redemption of shares						$ 1,000,000.0
Forecast
Summary of Significant Accounting Policies [Line Items]
Remaining authorized repurchase amount					$ 800,000