Debt and Lines of Credit (Details) (USD $)						9 Months Ended		9 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended		9 Months Ended
	Sep. 30, 2014		Apr. 30, 2014	Dec. 31, 2013		Sep. 30, 2014 Bonds Private Placement - Fixed Rate [Member]	Dec. 31, 2013 Bonds Private Placement - Fixed Rate [Member]	Sep. 30, 2014 Term Loan - Variable Rate [Member]	Dec. 31, 2013 Term Loan - Variable Rate [Member]	Sep. 30, 2014 Unsecured Bonds - Fixed Rate [Member]	Dec. 31, 2013 Unsecured Bonds - Fixed Rate [Member]	Aug. 31, 2014 Mortgage Notes [Member] Apartment	Sep. 30, 2014 Mortgage Notes [Member]	Dec. 31, 2013 Mortgage Notes [Member]	Sep. 30, 2014 Line of Credit [Member]	Dec. 31, 2013 Line of Credit [Member]
Debt Instrument [Line Items]
Aggregate principal amount of senior notes assumed			$ 900,000,000									$ 21,500,000
Principal balance on debt			711,300,000
Premium on debt assumed	118,940		124,500,000	6,553								2,100,000
Unsecured debts and line of credit [Abstract]
Unsecured debt	2,745,487,000			1,410,023,000		465,000,000	465,000,000	350,000,000	350,000,000	1,930,487,000	595,023,000		2,258,010,000	1,404,080,000
Lines of credit	222,628,000			219,421,000
Total unsecured debt and lines of credit	5,226,125,000	[1]		3,033,524,000	[1]
Number of units												220
Weighted Average Maturity						4 years 6 months		2 years 4 months 24 days		7 years 3 months 18 days		10 years
Weighted Average Maturity, Line of credit													5 years 9 months 18 days		4 years 6 months
Unamortized premium	118,940		124,500,000	6,553								2,100,000
Weighted average interest rate (in hundredths)			3.30%					2.40%	2.50%	3.60%	4.00%		4.60%	4.70%	1.70%	2.20%
Fixed interest rate												5.50%
Aggregate schedule principal payments [Abstract]
Remaining in 2014	7,388,000
2015	94,580,000
2016	391,481,000
2017	688,683,000
2018	320,080,000
Thereafter	3,382,345,000
Total	$ 4,884,557,000

[1] Includes total unamortized premium of $118,940 and $6,553 as of September 30, 2014 and December 31, 2013, respectively.