Supplemental Disclosures of Cash Flow Information (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
item
Supplemental Disclosures of Cash Flow Information    
Loans receivable   $ 48,900,000
Number of acquired properties   5
Cash paid for interest 85,900,000 79,900,000
Interest capitalized to properties under development 94,000 95,000
Cash paid for income taxes 1,800,000 942,000
Non-cash investing and financing activities    
Loans Assumed   45,900,000
Net discounts recorded on mortgages assumed   2,800,000
Interest rate swap agreement acquired   901,000
Increase in buildings and improvements and accounts payable   $ 7,100,000