Real Estate and Mortgage Notes Receivable Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 sqft MortgageLoan PropertyAndMortgageLoan JointVenture Property	Dec. 31, 2011
Owned properties:
Total number of company owned real estate properties	198
Gross investment, amount, total	$ 2,887,598
Number of investment, whole units	6
Gross Investment, Amount	2,768,273	2,788,618
Gross Investment, %	95.90%
Square footage of owned real estate properties	13,500,000
Square Feet, whole units	13,478,000
Square Feet, %	100.00%
Mortgage notes receivable:
Mortgage Loans on Real Estate	118,059	97,381
Gross Investment, %	4.10%
Unconsolidated joint venture:
Number of investments, whole units	1
Gross Investment, Amount	1,266	1,266
Gross investment, amount, total	2,887,598
Real estate properties and mortgages	205
Gross Investment, % total	100.00%
Square footage of owned real estate properties	13,500,000
Real Estate Investment Square Feet Footage Percentage	100.00%
Medical office/outpatient [Member]
Mortgage notes receivable:
Number of investments, whole units	4
Mortgage Loans on Real Estate	41,801
Gross Investment, %	1.40%
Inpatient [Member]
Mortgage notes receivable:
Number of investments, whole units	1
Mortgage Loans on Real Estate	36,258
Gross Investment, %	1.30%
Other [Member]
Owned properties:
Gross investment, amount, total	1,266
Mortgage notes receivable:
Number of investments, whole units	1
Mortgage Loans on Real Estate	40,000
Gross Investment, %	1.40%
Unconsolidated joint venture:
Number of investments, whole units	1
Gross investment, amount, total	1,266
Multi Tenanted with Occupancy Leases [Member]
Owned properties:
Total number of company owned real estate properties	161
Gross Investment, Amount	2,181,349
Gross Investment, %	75.60%
Square Feet, whole units	11,206,000
Square Feet, %	83.10%
Multi Tenanted with Occupancy Leases [Member] | Medical office/outpatient [Member]
Owned properties:
Total number of company owned real estate properties	148
Gross Investment, Amount	1,782,088
Gross Investment, %	61.80%
Square Feet, whole units	9,764,000
Square Feet, %	72.40%
Multi Tenanted with Occupancy Leases [Member] | Medical Office - Stabilization in Progress [Member]
Owned properties:
Total number of company owned real estate properties	11
Gross Investment, Amount	379,494
Gross Investment, %	13.10%
Square Feet, whole units	1,186,000
Square Feet, %	8.80%
Multi Tenanted with Occupancy Leases [Member] | Other [Member]
Owned properties:
Total number of company owned real estate properties	2
Gross Investment, Amount	19,767
Gross Investment, %	0.70%
Square Feet, whole units	256,000
Square Feet, %	1.90%
Single Tenant Net Leases [Member]
Owned properties:
Total number of company owned real estate properties	36
Gross Investment, Amount	537,940
Gross Investment, %	18.60%
Square Feet, whole units	2,176,000
Square Feet, %	16.20%
Single Tenant Net Leases [Member] | Medical office/outpatient [Member]
Owned properties:
Total number of company owned real estate properties	20
Gross Investment, Amount	190,903
Gross Investment, %	6.60%
Square Feet, whole units	982,000
Square Feet, %	7.30%
Single Tenant Net Leases [Member] | Inpatient [Member]
Owned properties:
Total number of company owned real estate properties	14
Gross Investment, Amount	337,492
Gross Investment, %	11.70%
Square Feet, whole units	1,103,000
Square Feet, %	8.20%
Single Tenant Net Leases [Member] | Other [Member]
Owned properties:
Total number of company owned real estate properties	2
Gross Investment, Amount	9,545
Gross Investment, %	0.30%
Square Feet, whole units	91,000
Square Feet, %	0.70%
Property Operating Agreements [Member]
Unconsolidated joint venture:
Gross Investment, Amount	73,600
Land Held for Development and Corporate Property [Member]
Owned properties:
Gross Investment, Amount	25,171
Gross Investment, %	0.90%
Corporate Property [Member]
Owned properties:
Gross Investment, Amount	14,804
Gross Investment, %	0.50%
Medical Office - Construction in Progress [Member]
Owned properties:
Total number of company owned real estate properties	1
Gross Investment, Amount	34,180
Gross Investment, %	1.20%
Square Feet, whole units	96,000
Square Feet, %	0.70%
Medical Office - Construction in Progress [Member] | Medical office/outpatient [Member]
Owned properties:
Total number of company owned real estate properties	1
Gross Investment, Amount	$ 9,009
Gross Investment, %	0.30%
Square Feet, whole units	96,000
Square Feet, %	0.70%