Supplemental Disclosures of Cash Flow Information (Details)	6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($) item
Supplemental Disclosures of Cash Flow Information
Loans receivable		$ 48,900,000
Number of acquired properties | item		5
Cash paid for interest	$ 114,600,000	$ 104,200,000
Interest capitalized to properties under development	266,000	220,000
Cash paid for income taxes	$ 3,100,000	2,900,000
Non-cash investing and financing activities
Loans Acquired		159,700,000
Net premiums recorded upon acquisition of mortgages		718,000
Interest rate swap agreement acquired		901,000
Increase in buildings and improvements and accounts payable		$ 3,900,000