REAL ESTATE AND OTHER AFFILIATES (Narrative) (Details)	3 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2015 USD ($) item	Sep. 30, 2018 USD ($) item	Dec. 31, 2017 USD ($) item
Real Estate and Other Affiliates
Number of variable interest entities in which entity is primary beneficiary | item			4	3
Carrying values of the assets associated with the operations of the consolidated VIEs			$ 154,200,000	$ 24,800,000
Carrying values of the liabilities associated with the operations of the consolidated VIEs			$ 90,500,000	$ 2,700,000
USAA Joint Venture
Real Estate and Other Affiliates
Contribution of property	$ 33,600,000
Fair value of property contributed	85,000,000
Joint venture capital obligations	$ 42,700,000
Equity ownership in joint venture	33.00%
Preferred return on capital	9.00%
Joint Venture Real Estate, Ownership Percentage			90.00%
The Summit
Real Estate and Other Affiliates
Preferred return on capital		5.00%
Cash distribution entitlement by the joint venture | item		2
Equity Method Investments | The Summit
Real Estate and Other Affiliates
Contribution of property		$ 13,400,000
SID bonds transferred to joint venture		1,300,000
Transaction value of land contributed to joint venture		125,400,000
Transactional value per acre of land contributed to joint venture		226,000
Maximum contribution required to joint venture by co-venturer		$ 30,000,000.0
Unconsolidated Properties
Real Estate and Other Affiliates
Secured debt real estate affiliates			$ 199,800,000
Share of entity in secured debt			$ 94,900,000
USAA | USAA Joint Venture
Real Estate and Other Affiliates
Capital contribution to joint venture	$ 64,000,000
Joint venture capital obligations	$ 105,600,000
Preferred return on capital	9.00%
Joint Venture Real Estate, Ownership Percentage			10.00%
Preferred return on capital of cash distribution	11.11%