CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Real estate:
Land	$ 3,287,607	$ 1,440,590
Buildings and improvements	11,188,804	7,185,853
Furniture, fixtures and equipment	318,423	255,733
Total Capitalized Cost	14,794,834	8,882,176
Less accumulated depreciation	(2,143,581)	(2,034,364)
Net operating real estate	12,651,253	6,847,812
Construction in progress, including land	1,003,898	802,883
Land held for development	359,029	316,037
Operating real estate assets held for sale, net		48,388
Total real estate, net	14,014,180	8,015,120
Cash and cash equivalents	447,456	2,733,618
Cash in escrow	93,650	50,033
Resident security deposits	27,313	24,748
Investments in unconsolidated real estate entities	371,983	129,352
Deferred financing costs, net	36,606	38,700
Deferred development costs	33,275	24,665
Prepaid expenses and other assets	162,901	143,842
Total assets	15,187,364	11,160,078
LIABILITIES AND EQUITY
Unsecured notes, net	1,845,961	1,945,798
Variable rate unsecured credit facility	0
Mortgage notes payable, net	4,082,328	1,905,235
Dividends payable	138,438	110,966
Payables for construction	53,317	53,677
Accrued expenses and other liabilities	316,618	224,194
Accrued interest payable	24,290	33,056
Resident security deposits	46,755	38,626
Liabilities related to real estate assets held for sale		706
Total liabilities	6,507,707	4,312,258
Redeemable noncontrolling interests	20,769	7,027
Equity:
Preferred stock, $0.01 par value; $25 liquidation preference; 50,000,000 shares authorized at both March 31, 2013 and December 31, 2012; zero shares issued and outstanding at March 31, 2013 and December 31, 2012, respectively
Common stock, $0.01 par value; 140,000,000 shares authorized at both March 31, 2013 and December 31, 2012; 129,382,118 and 114,403,472 shares issued and outstanding at March 31, 2013 and December 31, 2012, respectively	1,294	1,144
Additional paid-in capital	8,967,298	7,086,407
Accumulated earnings less dividends	(206,667)	(142,329)
Accumulated other comprehensive loss	(106,616)	(108,007)
Total equity	8,655,309	6,837,215
Noncontrolling interest	3,579	3,578
Total equity	8,658,888	6,840,793
Total liabilities and equity	$ 15,187,364	$ 11,160,078