Real Estate and Mortgage Notes Receivable Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Owned properties:
Number of investments, whole units	203
Gross Investment, Amount	$ 2,615,248	$ 2,571,605
Gross Investment, %	95.40%
Square Feet, whole units	13,388,000
Square Feet, %	100.00%
Mortgage loans:
Number of investments, whole units	12
Mortgage notes receivable	122,603	36,599
Gross Investment, %	4.50%
Unconsolidated joint venture
Number of investments, whole units	1
Gross Investment, Amount	1,266	1,300
Gross Investment, %	0.10%
Number of investments, total whole units	216
Gross investment, amount, total	2,739,117
Gross Investment, %, total	100.00%
Square Footage of Real Estate Property	13,400,000
Master Leases [Member]
Owned properties:
Number of investments, whole units	43
Gross Investment, Amount	559,110
Gross Investment, %	20.20%
Square Feet, whole units	2,368,000
Square Feet, %	17.60%
Master Leases [Member] | Medical office/outpatient [Member]
Owned properties:
Number of investments, whole units	27
Gross Investment, Amount	220,777
Gross Investment, %	7.90%
Square Feet, whole units	1,204,000
Square Feet, %	9.00%
Master Leases [Member] | Inpatient [Member]
Owned properties:
Number of investments, whole units	14
Gross Investment, Amount	328,788
Gross Investment, %	12.00%
Square Feet, whole units	1,072,000
Square Feet, %	7.90%
Multi-Tenanted With Occupancy Leases [Member]
Owned properties:
Number of investments, whole units	149
Gross Investment, Amount	1,853,295
Gross Investment, %	67.80%
Square Feet, whole units	10,018,000
Square Feet, %	74.80%
Multi-Tenanted With Occupancy Leases [Member] | Medical office/outpatient [Member]
Owned properties:
Number of investments, whole units	139
Gross Investment, Amount	1,598,621
Gross Investment, %	58.50%
Square Feet, whole units	8,954,000
Square Feet, %	66.90%
Multi-Tenanted With Occupancy Leases [Member] | Medical Office - Stabilization In Progress [Member]
Owned properties:
Number of investments, whole units	8
Gross Investment, Amount	235,026
Gross Investment, %	8.60%
Square Feet, whole units	808,000
Square Feet, %	6.00%
Multi-Tenanted With Occupancy Leases [Member] | Medical Office - Construction In Progress [Member]
Owned properties:
Number of investments, whole units	3
Gross Investment, Amount	83,968
Gross Investment, %	3.10%
Square Feet, whole units	378,000
Square Feet, %	29.00%
Multi-Tenanted With Occupancy Leases [Member] | Other [Member]
Owned properties:
Number of investments, whole units	2
Gross Investment, Amount	19,648
Gross Investment, %	0.70%
Square Feet, whole units	256,000
Square Feet, %	1.90%
Property Operating Agreements [Member]
Owned properties:
Number of investments, whole units	8
Gross Investment, Amount	83,065
Gross Investment, %	3.00%
Square Feet, whole units	624,000
Square Feet, %	4.70%
Property Operating Agreements [Member] | Medical office/outpatient [Member]
Owned properties:
Number of investments, whole units	8
Gross Investment, Amount	83,065
Gross Investment, %	3.00%
Square Feet, whole units	624,000
Square Feet, %	4.70%
Land Held for Development and Corporate Property [Member]
Owned properties:
Gross Investment, Amount	20,773
Gross Investment, %	0.80%
Corporate Property [Member]
Owned properties:
Gross Investment, Amount	15,037
Gross Investment, %	0.50%
Medical office/outpatient [Member]
Mortgage loans:
Number of investments, whole units	9
Mortgage notes receivable	49,714
Gross Investment, %	1.80%
Medical Office - Construction In Progress [Member]
Owned properties:
Number of investments, whole units	3
Gross Investment, Amount	104,741
Gross Investment, %	3.90%
Square Feet, whole units	378,000
Square Feet, %	29.00%
Inpatient [Member]
Mortgage loans:
Number of investments, whole units	2
Mortgage notes receivable	32,889
Gross Investment, %	1.20%
Other [Member]
Owned properties:
Number of investments, whole units	2
Gross Investment, Amount	9,545
Gross Investment, %	0.30%
Square Feet, whole units	92,000
Square Feet, %	0.70%
Mortgage loans:
Number of investments, whole units	1
Mortgage notes receivable	40,000
Gross Investment, %	1.50%
Unconsolidated joint venture
Number of investments, whole units	1
Gross Investment, Amount	$ 1,266
Gross Investment, %	0.10%