Subsequent Events (Details) (USD $)	9 Months Ended							1 Months Ended
	Sep. 30, 2012 sqft	Sep. 30, 2011	Dec. 31, 2011 sqft	Jan. 31, 2011 sqft	Oct. 31, 2012 Subsequent Event [Member]	Nov. 24, 2012 Subsequent Event [Member] Accrued and Unpaid Interest [Member]	Nov. 24, 2012 Subsequent Event [Member] Make-Whole Premium [Member]	Oct. 31, 2012 Contract to Acquire Property [Member] Subsequent Event [Member]	Oct. 31, 2012 Retail Condominium [Member] Subsequent Event [Member]	Oct. 31, 2012 Parcel of Land [Member] Subsequent Event [Member]	Oct. 31, 2012 Real Estate [Member] Contract to Acquire Property [Member] Subsequent Event [Member] acre	Oct. 31, 2012 Retail Site [Member] Contract to Acquire Property [Member] Subsequent Event [Member] sqft	Oct. 31, 2012 Apartment Building [Member] Contract to Acquire Property [Member] Subsequent Event [Member] sqft	Oct. 31, 2012 Assisted Living Facility [Member] Contract to Acquire Property [Member] Subsequent Event [Member] units	Oct. 25, 2012 Senior Unsecured Notes 3.75 Percent Due 2022 [Member] Subsequent Event [Member] Unsecured Debt [Member]	Oct. 25, 2012 Senior Notes 6.25 Percent Due 2014 [Member] Subsequent Event [Member] Senior Notes [Member]
Subsequent Event [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price					$ 29,500,000				$ 27,500,000	$ 2,000,000
Business Acquisition, Cost of Acquired Entity, Liabilities Incurred									16,700,000
Square Feet/Acres	16,700,000		3,900,000	2,600,000							22	214,767	211,020
Number of Units in Real Estate Property														62
Mortgage Loans on Real Estate								95,000,000
Mezzanine loan interest rate								5.00%
Cash paid for income producing properties	234,485,000	144,255,000						140,000,000
Debt Instrument, Face Amount															300,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage															3.75%	6.25%
Debt Instrument, Redemption Amount						6,900,000	27,800,000
Debt Instrument, Offer Price, Percentage															99.591%
Debt Instrument, Yield To Maturity															3.799%
Debt Instrument, Spread over Treasury Note, Percentage															2.00%
Financing Receivable, Net	$ 64,687,000		$ 45,279,000