REAL ESTATE AND RELATED LEASE INTANGIBLES, NET - Schedule of Real Estate Properties Acquired (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Purchase Price	$ 236,932	$ 62,495	$ 219,456
Real estate acquired in settlement of mortgage loan receivable held for investment	0	0	6,700
Land | St. Paul, MN
Business Acquisition [Line Items]
Purchase Price		$ 200
Ownership Interest (percent)		100.00%
Net Lease | Carmi, IL
Business Acquisition [Line Items]
Purchase Price	$ 1,411
Ownership Interest (percent)	100.00%
Net Lease | Peoria, IL
Business Acquisition [Line Items]
Purchase Price	$ 1,183		$ 1,226
Ownership Interest (percent)	100.00%		100.00%
Net Lease | Ridgedale, MO
Business Acquisition [Line Items]
Purchase Price	$ 1,298
Ownership Interest (percent)	100.00%
Net Lease | Hanna City, IL
Business Acquisition [Line Items]
Purchase Price	$ 1,141
Ownership Interest (percent)	100.00%
Net Lease | Jessup, IA
Business Acquisition [Line Items]
Purchase Price	$ 1,163
Ownership Interest (percent)	100.00%
Net Lease | Shelbyville, IL
Business Acquisition [Line Items]
Purchase Price	$ 1,132
Ownership Interest (percent)	100.00%
Net Lease | Jacksonville, FL
Business Acquisition [Line Items]
Purchase Price	$ 115,641
Ownership Interest (percent)	100.00%
Net Lease | Wabasha, MN
Business Acquisition [Line Items]
Purchase Price	$ 1,280
Ownership Interest (percent)	100.00%
Net Lease | Port O'Connor, TX
Business Acquisition [Line Items]
Purchase Price	$ 1,255
Ownership Interest (percent)	100.00%
Net Lease | Denver, IA
Business Acquisition [Line Items]
Purchase Price	$ 1,183
Ownership Interest (percent)	100.00%
Net Lease | Jefferson City, MO
Business Acquisition [Line Items]
Purchase Price	$ 1,241
Ownership Interest (percent)	100.00%
Net Lease | Milford, IA
Business Acquisition [Line Items]
Purchase Price	$ 1,298
Ownership Interest (percent)	100.00%
Net Lease | Kawkawlin, MI
Business Acquisition [Line Items]
Purchase Price	$ 1,234
Ownership Interest (percent)	100.00%
Net Lease | Aroma Park, IL
Business Acquisition [Line Items]
Purchase Price	$ 1,218
Ownership Interest (percent)	100.00%
Net Lease | East Peoria, IL
Business Acquisition [Line Items]
Purchase Price	$ 1,350
Ownership Interest (percent)	100.00%
Net Lease | Winterset, IA
Business Acquisition [Line Items]
Purchase Price	$ 1,258
Ownership Interest (percent)	100.00%
Net Lease | Rockford, MN
Business Acquisition [Line Items]
Purchase Price	$ 1,195
Ownership Interest (percent)	100.00%
Net Lease | Dimmitt, TX
Business Acquisition [Line Items]
Purchase Price		$ 1,319
Ownership Interest (percent)		100.00%
Net Lease | Philo, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,156
Ownership Interest (percent)		100.00%
Net Lease | St. Charles, MN
Business Acquisition [Line Items]
Purchase Price		$ 1,198
Ownership Interest (percent)		100.00%
Net Lease | San Antonio, TX
Business Acquisition [Line Items]
Purchase Price		$ 1,096
Ownership Interest (percent)		100.00%
Net Lease | Borger, TX
Business Acquisition [Line Items]
Purchase Price		$ 978
Ownership Interest (percent)		100.00%
Net Lease | Champaign, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,324
Ownership Interest (percent)		100.00%
Net Lease | Decatur-Sunnyside, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,181
Ownership Interest (percent)		100.00%
Net Lease | Flora Vista, NM
Business Acquisition [Line Items]
Purchase Price		$ 1,305
Ownership Interest (percent)		100.00%
Net Lease | Mountain Grove, MO
Business Acquisition [Line Items]
Purchase Price		$ 1,279
Ownership Interest (percent)		100.00%
Net Lease | Rantoul, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,204
Ownership Interest (percent)		100.00%
Net Lease | Decatur-Pershing, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,365
Ownership Interest (percent)		100.00%
Net Lease | Cape Girardeau, MO
Business Acquisition [Line Items]
Purchase Price		$ 1,281
Ownership Interest (percent)		100.00%
Net Lease | Linn, MO
Business Acquisition [Line Items]
Purchase Price		$ 1,122
Ownership Interest (percent)		100.00%
Net Lease | Union, MO
Business Acquisition [Line Items]
Purchase Price		$ 1,227
Ownership Interest (percent)		100.00%
Net Lease | Pawnee, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,201
Ownership Interest (percent)		100.00%
Net Lease | Lamar, MO
Business Acquisition [Line Items]
Purchase Price		$ 1,176
Ownership Interest (percent)		100.00%
Net Lease | Dryden Township, MI
Business Acquisition [Line Items]
Purchase Price		$ 1,190
Ownership Interest (percent)		100.00%
Net Lease | Fayetteville, NC
Business Acquisition [Line Items]
Purchase Price		$ 6,971
Ownership Interest (percent)		100.00%
Net Lease | Springfield, IL
Business Acquisition [Line Items]
Purchase Price		$ 1,322
Ownership Interest (percent)		100.00%
Net Lease | Jacksonville, NC
Business Acquisition [Line Items]
Purchase Price			$ 7,877
Ownership Interest (percent)			100.00%
Net Lease | Iberia, MO
Business Acquisition [Line Items]
Purchase Price			$ 1,328
Ownership Interest (percent)			100.00%
Net Lease | Isle, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,078
Ownership Interest (percent)			100.00%
Net Lease | Pine Island, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,142
Ownership Interest (percent)			100.00%
Net Lease | Kings Mountain, NC
Business Acquisition [Line Items]
Purchase Price			$ 21,241
Ownership Interest (percent)			100.00%
Net Lease | Village of Menomonee Falls, WI
Business Acquisition [Line Items]
Purchase Price			$ 17,050
Ownership Interest (percent)			100.00%
Net Lease | Rockland, MA
Business Acquisition [Line Items]
Purchase Price			$ 7,316
Ownership Interest (percent)			100.00%
Net Lease | Crawfordsville, IA
Business Acquisition [Line Items]
Purchase Price			$ 6,000
Ownership Interest (percent)			100.00%
Net Lease | Boardman Township, OH
Business Acquisition [Line Items]
Purchase Price			$ 5,400
Ownership Interest (percent)			100.00%
Net Lease | Hilliard, OH
Business Acquisition [Line Items]
Purchase Price			$ 6,384
Ownership Interest (percent)			100.00%
Net Lease | Weathersfield Township, OH
Business Acquisition [Line Items]
Purchase Price			$ 5,200
Ownership Interest (percent)			100.00%
Net Lease | Rotterdam, NY
Business Acquisition [Line Items]
Purchase Price			$ 12,000
Ownership Interest (percent)			100.00%
Net Lease | Wheaton, MO
Business Acquisition [Line Items]
Purchase Price			$ 970
Ownership Interest (percent)			100.00%
Net Lease | Paynesville, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,254
Ownership Interest (percent)			100.00%
Net Lease | Loveland, CO
Business Acquisition [Line Items]
Purchase Price			$ 5,600
Ownership Interest (percent)			100.00%
Net Lease | Battle Lake, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,098
Ownership Interest (percent)			100.00%
Net Lease | Yorktown, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,207
Ownership Interest (percent)			100.00%
Net Lease | St. Francis, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,117
Ownership Interest (percent)			100.00%
Net Lease | Red Oak, IA
Business Acquisition [Line Items]
Purchase Price			$ 1,185
Ownership Interest (percent)			100.00%
Net Lease | Zapata, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,150
Ownership Interest (percent)			100.00%
Net Lease | Aurora, MN
Business Acquisition [Line Items]
Purchase Price			$ 952
Ownership Interest (percent)			100.00%
Net Lease | Canyon Lake, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,377
Ownership Interest (percent)			100.00%
Net Lease | Wheeler, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,075
Ownership Interest (percent)			100.00%
Net Lease | Bridgeport, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,186
Ownership Interest (percent)			100.00%
Net Lease | Pleasanton, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,316
Ownership Interest (percent)			100.00%
Net Lease | Warren, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,055
Ownership Interest (percent)			100.00%
Net Lease | Tremont, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,150
Ownership Interest (percent)			100.00%
Net Lease | Ponce, Puerto Rico
Business Acquisition [Line Items]
Purchase Price			$ 8,900
Ownership Interest (percent)			100.00%
Net Lease | Effingham County, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,195
Ownership Interest (percent)			100.00%
Net Lease | Lebanon, MI
Business Acquisition [Line Items]
Purchase Price			$ 1,200
Ownership Interest (percent)			100.00%
Net Lease | Minot, ND
Business Acquisition [Line Items]
Purchase Price			$ 6,644
Ownership Interest (percent)			100.00%
Net Lease | Floresville, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,251
Ownership Interest (percent)			100.00%
Net Lease | Kerrville, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,174
Ownership Interest (percent)			97.00%
Net Lease | De Soto, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,066
Ownership Interest (percent)			97.00%
Net Lease | Biscoe, NC
Business Acquisition [Line Items]
Purchase Price			$ 1,216
Ownership Interest (percent)			100.00%
Net Lease | Moultrie, GA
Business Acquisition [Line Items]
Purchase Price			$ 1,305
Ownership Interest (percent)			100.00%
Net Lease | Rose Hill, NC
Business Acquisition [Line Items]
Purchase Price			$ 1,420
Ownership Interest (percent)			100.00%
Net Lease | Rockingham, NC
Business Acquisition [Line Items]
Purchase Price			$ 1,158
Ownership Interest (percent)			100.00%
Net Lease | Wilmington, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,309
Ownership Interest (percent)			100.00%
Net Lease | Danville, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,074
Ownership Interest (percent)			100.00%
Net Lease | Bloomington, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,193
Ownership Interest (percent)			100.00%
Net Lease | Lincoln County , MO
Business Acquisition [Line Items]
Purchase Price			$ 1,072
Ownership Interest (percent)			100.00%
Net Lease | Montrose, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,167
Ownership Interest (percent)			100.00%
Net Lease | Jenks, OK
Business Acquisition [Line Items]
Purchase Price			$ 12,160
Ownership Interest (percent)			100.00%
Net Lease | Grove, OK
Business Acquisition [Line Items]
Purchase Price			$ 5,030
Ownership Interest (percent)			100.00%
Net Lease | Farmington, IL
Business Acquisition [Line Items]
Purchase Price			$ 1,303
Ownership Interest (percent)			100.00%
Net Lease | Bixby, OK
Business Acquisition [Line Items]
Purchase Price			$ 10,978
Ownership Interest (percent)			100.00%
Net Lease | Rice, MN
Business Acquisition [Line Items]
Purchase Price			$ 1,200
Ownership Interest (percent)			100.00%
Net Lease | Gordonville, MO
Business Acquisition [Line Items]
Purchase Price			$ 1,125
Ownership Interest (percent)			100.00%
Net Lease | Malone, NY
Business Acquisition [Line Items]
Purchase Price			$ 1,466
Ownership Interest (percent)			100.00%
Net Lease | Mercedes, TX
Business Acquisition [Line Items]
Purchase Price			$ 1,204
Ownership Interest (percent)			100.00%
Net Lease | Albion, PA
Business Acquisition [Line Items]
Purchase Price			$ 1,525
Ownership Interest (percent)			100.00%
Net Lease | Radford, VA
Business Acquisition [Line Items]
Purchase Price			$ 1,564
Ownership Interest (percent)			100.00%
Net Lease | Rural Retreat, VA
Business Acquisition [Line Items]
Purchase Price			$ 1,399
Ownership Interest (percent)			100.00%
Net Lease | Mount Vernon, AL
Business Acquisition [Line Items]
Purchase Price			$ 1,224
Ownership Interest (percent)			100.00%
Other
Business Acquisition [Line Items]
Real estate acquired in settlement of mortgage loan receivable held for investment			$ 6,700
Other | Peoria, IL
Business Acquisition [Line Items]
Purchase Price		$ 2,760
Ownership Interest (percent)		100.00%
Other | El Monte, CA
Business Acquisition [Line Items]
Purchase Price	$ 54,110
Ownership Interest (percent)	70.00%
Other | Miami, FL
Business Acquisition [Line Items]
Purchase Price	$ 38,145
Ownership Interest (percent)	80.00%
Other | Crum Lynne, PA
Business Acquisition [Line Items]
Purchase Price	$ 9,196
Ownership Interest (percent)	100.00%
Other | Ewing, NJ
Business Acquisition [Line Items]
Purchase Price		$ 30,640
Ownership Interest (percent)		100.00%
Other | Grand Rapids, MI
Business Acquisition [Line Items]
Purchase Price			$ 9,300
Ownership Interest (percent)			97.00%
Other | Grand Rapids, MI
Business Acquisition [Line Items]
Purchase Price			$ 6,300
Ownership Interest (percent)			97.00%
Other | Wayne, NJ
Business Acquisition [Line Items]
Purchase Price			$ 9,700
Ownership Interest (percent)			100.00%
Other | Carmel, NY
Business Acquisition [Line Items]
Ownership Interest (percent)			100.00%
Real estate acquired in settlement of mortgage loan receivable held for investment			$ 6,700
Real Estate
Business Acquisition [Line Items]
Purchase Price			$ 212,756
Consolidated Joint Venture | Other | El Monte, CA
Business Acquisition [Line Items]
Purchase Price	$ 5,300
Consolidated Joint Venture | Other | Miami, FL
Business Acquisition [Line Items]
Purchase Price	$ 1,600