Acquisitions, Dispositions, and Mortgage Funding (Details Textual) (USD $)	3 Months Ended				1 Months Ended									3 Months Ended	1 Months Ended	3 Months Ended			1 Months Ended	3 Months Ended
	Mar. 31, 2013 Property		Dec. 31, 2012 Property		Mar. 31, 2013 Texas [Member] Land Disposed March 2013 [Member] acre	Jan. 31, 2013 Florida [Member] Inpatient Rehabilitation Hospital Potential Disposition July 2013 [Member] hospital	Jan. 31, 2013 Alabama [Member] Inpatient Rehabilitation Hospital Potential Disposition July 2013 [Member] hospital	Mar. 31, 2013 Florida and Alabama [Member] Inpatient Rehabilitation Hospital Potential Disposition July 2013 [Member] hospital	Jan. 31, 2013 Florida and Alabama [Member] Inpatient Rehabilitation Hospital Potential Disposition July 2013 [Member] hospital	Apr. 30, 2013 Pennsylvania Inpatient Rehabilitation Hospital Potential Disposition September 2013 [Member] Subsequent Event [Member] hospital	Mar. 31, 2013 Mortgage Loan Receivable Due March 2015 [Member] Texas [Member] Land Disposed March 2013 [Member]	Mar. 31, 2013 Mortgage Loan Receivable Due March 2015 [Member] Texas [Member] Land Disposed March 2013 [Member] First Year [Member]	Mar. 31, 2013 Mortgage Loan Receivable Due March 2015 [Member] Texas [Member] Land Disposed March 2013 [Member] Second Year [Member]	Mar. 31, 2013 Texas [Member]	Jan. 31, 2013 Real Estate Acquisitions [Member] Tennesee [Member] Tenant sqft	Mar. 31, 2013 Real Estate Acquisitions [Member] Tennesee [Member]	Oct. 31, 2012 Real Estate Acquisitions [Member] Tennesee [Member] sqft	Jan. 31, 2013 Real Estate Acquisitions [Member] Tennesee [Member] Market rate lease intangibles [Member]	Apr. 30, 2013 Real Estate Acquisitions [Member] Texas [Member] Subsequent Event [Member] Tenant sqft	Mar. 31, 2013 Mortgage Note Financing [Member] Oklahoma and Missouri [Member] Facility mortgage_note_receivable	Mar. 31, 2013 Mortgage Note Financing [Member] Oklahoma and Missouri [Member] Scenario, Forecast [Member]
Acquisitions and Dispositions [Line Items]
Date of asset acquisition															Jan. 29, 2013
Square footage															52,225		39,345		42,627
Cash consideration															$ 16,200,000				$ 16,300,000
Intangible acquired in acquisition																		500,000
Percentage of property leased																100.00%			100.00%
Number of tenants occupying building															4				1
Area sold					15.1
Real estate investment disposed					8,100,000
Sales price					5,000,000
Proceeds from sale					1,100,000
Seller financed mortgage notes receivable											3,700,000
Closing costs					200,000
Interest rate												5.00%	6.00%
Gain (Loss) on Disposition of Assets					3,300,000
Number of leased properties, lessee purchase options						1	1	2	2	2
Leased properties, purchase option, minimum purchase price									29,400,000	17,600,000
Leased properties, purchase option, lease base rent per quarter								1,000,000		1,300,000
Payments to fund mortgage notes receivable																				24,300,000	59,900,000
Number of mortgage notes funded																				2
Number of developing build to suit facilities																				2
Mortgage notes receivable	190,134,000	[1]	162,191,000	[1]																142,700,000
Proceeds from noncontrolling interest														1,400,000
Real estate investment property	2,216,546,000		2,244,959,000					18,600,000		25,100,000
Noncontrolling interest, ownership percentage by parent														40.00%
Real estate investment property	2,813,980,000		2,831,684,000
Partnership, ownership percentage	60.00%
Partnership, consolidated mortgage loan	13,700,000
Partnership, permanent mortgage loan upon settlement of equity contributions	10,300,000
Number of properties held for sale	4		1
Impairment of long-lived assets held for sale	$ 0

[1] Level 2 - Fair value based on quoted prices for similar instruments in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations in which significant inputs and significant value drivers are observable in active markets.