Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 segment property	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Allowance for uncollectible accounts	$ 2,100,000	$ 2,200,000	$ 1,500,000
Bad debt expense	453,000	1,064,000	1,447,000
Depreciation expense	75,500,000	71,400,000	64,400,000
Number of properties held-for-sale	1
Impairment of real estate investments	0	0	0
Impairment of real estate notes receivable	0	0	0
Tax basis in excess of carrying amount of net assets	254,700,000
Cash in excess of FDIC insured limits	$ 19,900,000
Number of reportable segments	1
Minimum
Income Taxes
Percentage of income required to be distributed as dividends	90.00%
Buildings
Property, Plant and Equipment [Line Items]
Operating properties, estimated useful lives	39 years
Tenant Improvements | Minimum
Property, Plant and Equipment [Line Items]
Operating properties, estimated useful lives	1 month
Tenant Improvements | Maximum
Property, Plant and Equipment [Line Items]
Operating properties, estimated useful lives	240 months
Furniture, Fixtures and Equipment
Property, Plant and Equipment [Line Items]
Operating properties, estimated useful lives	5 years