Commitments and Contingencies - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 litigation_settlement sqft property	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Number of ground leases related to real estate investments under operating lease agreements	44
Operating lease expiration period maximum expiration date	2101
Approximately corporate office lease covers of rented space	30,934
Lease Expansion, Next Fiscal Year, Approximate Area	5,719
Percentage on increases of annual base rent on the corporate office lease	3.25%
Rental expense relating to the operating leases	$ 4,400,000	$ 4,300,000	$ 4,300,000
Prepaid ground leases which represented rental expense	500,000	500,000	400,000
Number of claims settled	1
General and Administrative Expense [Member]
Property, Plant and Equipment [Line Items]
Litigation expense	950,000
Construction mortgage loans [Member]
Property, Plant and Equipment [Line Items]
Anticipated amount of investment	14,900,000
Number of construction mortgages loans	1
Second Generation Leases [Member] | Tenant Improvement Allowances [Member]
Property, Plant and Equipment [Line Items]
Anticipated amount of investment	5,500,000
Corporate Office Lease [Member]
Property, Plant and Equipment [Line Items]
Corporate lease expiration date	Oct. 31, 2020
Minimum [Member] | First Generation Leases [Member] | Tenant Improvement Allowances [Member]
Property, Plant and Equipment [Line Items]
Anticipated amount of investment	26,500,000
Maximum [Member] | First Generation Leases [Member] | Tenant Improvement Allowances [Member]
Property, Plant and Equipment [Line Items]
Anticipated amount of investment	$ 31,700,000