Significant Transactions During the Second Quarter of 2014 and Subsequent Events (Details) (USD $)	3 Months Ended	6 Months Ended			3 Months Ended	6 Months Ended	0 Months Ended		6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended	1 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Common Stock [Member]	Jun. 30, 2014 Common Stock [Member]	May 13, 2014 4.875% Series G Cumulative Convertible Preferred Stock [Member]	May 13, 2014 4.875% Series G Cumulative Convertible Preferred Stock [Member]	Jun. 30, 2014 Common Stock EPT & EPL [Member]	Aug. 08, 2014 Subsequent Event [Member]	Jun. 30, 2014 Subsequent Event [Member]	Aug. 08, 2014 Subsequent Event [Member] Common Stock [Member]	Jun. 30, 2014 Subsequent Event [Member] Common Stock [Member]	Apr. 30, 2014 Unsecured Debt [Member]	May 31, 2014 Collins on Pine [Member] Unit	Jul. 31, 2014 Paragon Apartments [Member] Subsequent Event [Member] Apartment
Acquisitions [Abstract]
Cost of acquired entity		$ 555,826,000	$ 0												$ 29,200,000	$ 111,000,000
Number of units															76	301
Debt instrument assumed	2,250,510,000	2,250,510,000		1,404,080,000
Dispositions [Abstract]
Number of units disposed of															76	301
Ownership percentage (in hundredths)	50.00%	50.00%
Common Stock [Abstract]
Shares issued during the period (in shares)	792,700					1,644,000			2,115,887	362,532	362,532
Average share price (in dollars per share)					$ 179.50	$ 179.50			$ 174.82			$ 187.28	$ 187.28
Proceed from stock issuance, net of commissions		279,427,000	122,905,000		141,400,000				366,900,000			67,500,000	67,500,000
Series G Preferred Stock [Abstract]
Preferred stock shares outstanding (in shares)								178,249
Conversion rate of preferred stock (in hundredths)							4.875%
Conversion rate into shares of common stock (in shares)								0.19301
Common stock issued upon conversion (in shares)						34,000	34,403
Unsecured Bond Offering [Abstract]
Debt instrument, principal amount														400,000,000
Stated interest rate (in hundredths)														3.875%
Maturity date														Dec. 31, 2014
Net proceeds from issuance of debt														$ 394,000,000