ORGANIZATION (Details) (USD $)	9 Months Ended	12 Months Ended	30 Months Ended	9 Months Ended	12 Months Ended	30 Months Ended
	Sep. 30, 2013 MortgageLoans	Dec. 31, 2012	Sep. 30, 2013 MortgageLoans	Sep. 30, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Sep. 30, 2013 Common Stock [Member]	Feb. 04, 2010 Common Stock [Member]	Sep. 30, 2013 Office Properties [Member] properties	Sep. 30, 2013 Minimum [Member]	Feb. 04, 2010 Minimum [Member] Common Stock [Member]	Sep. 30, 2013 Maximum [Member]	Feb. 14, 2013 Maximum [Member] Common Stock [Member]	Feb. 04, 2010 Maximum [Member] Common Stock [Member]	Feb. 14, 2013 Maximum [Member] Common Stock [Member] Dividend Reinvestment Plan [Member]	Jan. 26, 2010 KBS Capital Advisors LLC [Member]
Organizational Structure [Line Items]
Partnership interest in Operating Partnership	0.10%
Partnership interest in the Operating Partnership and is its sole limited partner	99.90%
Common stock, shares issued	53,228,785	27,148,131	53,228,785												20,000
Common stock, purchase price per share															$ 10.00
Shares held by affiliate				20,000		20,000
Percent of portfolio allocated to core properties									0.00%		20.00%
Number of real estate properties								10
Number of first mortgage loan secured by a deed of trust	1		1
Stock offering, shares authorized for issuance							200,000,000			250,000			280,000,000
Shares of common stock authorized under dividend reinvestment plan, shares							80,000,000
Issuance of common stock, shares				26,250,057	16,755,000	53,453,100
Issuance of common stock, value	$ 260,710,000	$ 166,857,000	$ 531,600,000	$ 263,000	$ 167,000
Shares of common stock sold under dividend reinvestment plan, shares						1,467,331
Shares of common stock sold under dividend reinvestment plan, value			13,900,000
Redemptions of common stock, shares				169,403	74,912	244,315
Redemptions of common stock, value	1,644,000	740,000	2,400,000	2,000	1,000
Stock offering, shares authorized for issuance, value												2,000,000,000
Stock offering, shares authorized for dividend reinvestment plan, value														$ 760,000,000
Number of shares to be sold														80,000,000