INVESTMENTS IN REAL ESTATE SECURITIES - Summary of Real Estate Securities in an Unrealized Loss Position (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 3,396,295
Other Than Temporary Impairment - Amortized Cost Basis	(1,970)		(1,127)
After Impairment	2,307,696
Carrying Value - Total	2,324,915
Weighted Average Life (Years)	10 months 2 days
Securities in an Unrealized Loss Position Less than Twelve Months [Member]
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	1,297,224
Before Impairment - Amortized Cost Basis	494,733
Other Than Temporary Impairment - Amortized Cost Basis	(1,071)	[1]
After Impairment	493,662
Gross Unrealized Losses - Less than Twelve Months	(3,202)
Carrying Value - Less than Twelve Months	490,460
Number of Securities - Less than Twelve Months	70
Weighted Average Rating	AA-	[2]
Weighted Average Coupon	1.37%
Weighted Average Yield	2.20%
Weighted Average Life (Years)	7 years 2 months 19 days
Securities in an Unrealized Loss Position Twelve Months or Greater [Member]
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	128,605
Before Impairment - Amortized Cost Basis	123,794
Other Than Temporary Impairment - Amortized Cost Basis	0	[1]
After Impairment	123,794
Gross Unrealized Losses - Twelve or More Months	(1,730)
Carrying Value - Twelve or More Months	122,064
Number of Securities - Twelve or More Months	22
Weighted Average Rating	AA+	[2]
Weighted Average Coupon	2.39%
Weighted Average Yield	1.96%
Weighted Average Life (Years)	4 years 5 months 1 day
Securities in a Loss Position [Member]
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	1,425,829
Before Impairment - Amortized Cost Basis	618,527
Other Than Temporary Impairment - Amortized Cost Basis	(1,071)	[1]
After Impairment	617,456
Gross Unrealized Losses - Total	(4,932)
Carrying Value - Total	$ 612,524
Number of Securities - Total	92
Weighted Average Rating	AA	[2]
Weighted Average Coupon	1.57%
Weighted Average Yield	2.15%
Weighted Average Life (Years)	6 years 7 months 27 days

[1] This amount represents other-than-temporary impairment recorded on securities that are in an unrealized loss position as of March 31, 2015.

[2] The weighted average rating of securities in an unrealized loss position for less than twelve months excludes the rating of 20 bonds which either have never been rated or for which rating information is no longer provided.