SIGNIFICANT ACCOUNTING POLICIES (Details) shares in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	Jan. 31, 2019 USD ($)	Oct. 20, 2015	Dec. 31, 2018 USD ($) item shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Jan. 01, 2019 USD ($)	Mar. 31, 2018 USD ($)
Accounting policies
Return on investment in unconsolidated joint ventures			$ 4,248	$ 4,416	$ 57,578
Distributions received from unconsolidated entities			$ (42,683)	(116,329)	(66,116)
Document period end date			Dec. 31, 2018
Allocation of other comprehensive income/(loss)			$ 244	281
Significant Accounting Policies
Development costs excluding direct costs and capitalized interest			7,500	8,800	7,900
Interest capitalized during period			10,600	18,600	16,500
Notes receivable			$ 42,259	19,469
Number of extension options on loan | item			2
Extension period of option on loan		6 months
Proceeds from notes receivable	$ 5,600
Procceds from accrued interest	200
Note receivable interest income			$ 4,100	1,800	$ 1,800
Promoted interest received	$ 8,500
Minimum period units are outstanding prior to redemption (in years)			1 year
Deferred Tax Liabilities, Net			$ (100)
Deferred Tax Assets, Net				$ 100
U.S. federal corporate income tax rate			21.00%	35.00%	35.00%
One time tax benefit				$ (1,100)
Advertising expense			$ 6,700	6,200	$ 6,400
Minimum percentage of carrying value of real estate portfolio			0.10
Note due March 2019
Significant Accounting Policies
Notes receivable			$ 20,000
Note receivable interest rate			12.00%
Aggregate Commitment on Note Receivable							$ 20,000
Note due February 2020
Significant Accounting Policies
Notes receivable			$ 14,659	13,669
Note receivable interest rate			10.00%
Aggregate Commitment on Note Receivable			$ 16,400
Additional amount loaned			1,000
Note maturity public capital threshold			5,000
Note due October 2020
Significant Accounting Policies
Notes receivable			$ 2,000	2,000
Note receivable interest rate			8.00%
Aggregate Commitment on Note Receivable			$ 2,000
Note maturity public capital threshold			10,000
Note due August 2022
Significant Accounting Policies
Notes receivable			$ 5,600	$ 3,800
Note receivable interest rate			10.00%
Aggregate Commitment on Note Receivable			$ 10,000
Additional amount loaned			1,800
Note maturity public capital threshold			$ 25,000
OP/DownREIT Units
Significant Accounting Policies
Antidilutive securities | shares			24,548	24,821	25,130
Convertible preferred stock
Significant Accounting Policies
Antidilutive securities | shares			3,011	3,021	3,028
Stock options, unvested LTIP Units and unvested restricted stock
Significant Accounting Policies
Antidilutive securities | shares			1,304	1,806	1,925
Minimum
Significant Accounting Policies
Ownership (as a percent)			100.00%
Minimum | Buildings
Significant Accounting Policies
Estimated useful lives			35 years
Minimum | Building improvements
Significant Accounting Policies
Estimated useful lives			10 years
Minimum | Furniture, fixtures, equipment, and other assets
Significant Accounting Policies
Estimated useful lives			3 years
Maximum | Buildings
Significant Accounting Policies
Estimated useful lives			55 years
Maximum | Building improvements
Significant Accounting Policies
Estimated useful lives			35 years
Maximum | Furniture, fixtures, equipment, and other assets
Significant Accounting Policies
Estimated useful lives			10 years
ASU 2016-02 | Minimum
Accounting policies
Right-of-use asset						$ 85,000
Operating lease liability						85,000
ASU 2016-02 | Maximum
Accounting policies
Right-of-use asset						150,000
Operating lease liability						$ 150,000
ASU 2016-01
Accounting policies
Gain on investment			$ 2,100
Secured Debt
Accounting policies
Deferred finance costs, net			(1,462)
Noncontrolling Interests
Accounting policies
Allocation of other comprehensive income/(loss)			$ 200	$ 300	$ 100