CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Land and Land Improvements	$ 3,489,749	$ 3,446,843
Real estate:
Buildings and improvements	12,414,349	12,275,850
Furniture, fixtures and equipment	413,793	403,393
Total Capitalized Cost	16,317,891	16,126,086
Less accumulated depreciation	(2,989,899)	(2,890,530)
Net operating real estate	13,327,992	13,235,556
Construction in progress, including land	1,460,226	1,417,246
Land held for development	536,538	180,516
Operating real estate assets held for sale, net	59,596	102,422
Real Estate Investments, Net	15,384,352	14,935,740
Cash and cash equivalents	194,928	508,276
Cash in escrow	102,788	95,625
Resident security deposits	29,514	29,563
Investments in unconsolidated real estate entities	262,050	298,315
Deferred financing costs, net	38,818	39,728
Deferred development costs	23,896	67,029
Prepaid expenses and other assets	227,402	202,447
Total assets	16,263,748	16,176,723
LIABILITIES AND EQUITY
Unsecured notes, net	3,043,509	2,993,265
Variable rate unsecured credit facility	0	0
Mortgage notes payable	3,518,822	3,532,587
Dividends payable	165,241	153,207
Payables for construction	94,131	101,930
Accrued expenses and other liabilities	249,682	244,017
Accrued interest payable	32,937	41,318
Resident security deposits	50,673	49,449
Liabilities related to real estate assets held for sale	733	1,780
Total liabilities	7,155,728	7,117,553
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount	10,508	12,765
Equity:
Preferred stock, $0.01 par value; $25 liquidation preference; 50,000,000 shares authorized at March 31, 2015 and December 31, 2014; zero shares issued and outstanding at March 31, 2015 and December 31, 2014	0	0
Common stock, $0.01 par value; 280,000,000 shares authorized at March 31, 2015 and December 31, 2014; 132,189,626 and 132,050,382 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	1,322	1,320
Additional paid-in capital	9,360,470	9,354,685
Accumulated earnings less dividends	(223,330)	(267,085)
Accumulated other comprehensive loss	(40,950)	(42,515)
Total equity	9,097,512	9,046,405
Total liabilities and equity	$ 16,263,748	$ 16,176,723