UNSECURED DEBT (Details)	1 Months Ended			9 Months Ended
	Jul. 31, 2015 USD ($)	May. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2015 USD ($) extension_option	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Mortgage and other notes payable				$ 1,111,753,000	$ 1,003,381,000
Number of extensions | extension_option				1
Length of extension				6 months
Convertible Debt
Debt Instrument [Line Items]
Outstanding convertible notes redeemed				$ 400,000
Line of Credit | Unsecured Credit Facility
Debt Instrument [Line Items]
Amount borrowed on unsecured credit facility				33,500,000
Line of credit, outstanding balance				33,500,000
Line of Credit | Unsecured term loan
Debt Instrument [Line Items]
Unsecured term loan	$ 50,000,000
Fund IV | Line of Credit | Unsecured Credit Facility
Debt Instrument [Line Items]
Debt instrument face amount			$ 50,000,000
Commitment fee threshold				20,000,000.0
Long-term line of credit				34,500,000
Unused capacity over threshold commitment fee percentage			1.00%
Unused capacity under threshold commitment fee percentage			2.75%
Fund IV | Line of Credit | Subscription Line | Line of Credit
Debt Instrument [Line Items]
Amount repaid on subscription line				52,100,000
Mortgage and other notes payable				25,000,000
Fund II | Line of Credit | Unsecured Credit Facility
Debt Instrument [Line Items]
Amount borrowed on unsecured credit facility		$ 12,500,000
Basis spread on variable rate		2.75%
Debt instrument face amount		$ 25,000,000
Commitment fee threshold				$ 12,500,000.0
Unused capacity commitment fee percentage		2.75%
LIBOR | Line of Credit | Unsecured term loan
Debt Instrument [Line Items]
Basis spread on variable rate	1.30%
LIBOR | Fund IV | Line of Credit | Unsecured Credit Facility
Debt Instrument [Line Items]
Basis spread on variable rate			2.75%