Investments In and Advances To Unconsolidated Affiliates (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) property	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)
Income Statements:
Rental and other revenues	$ 11,210		$ 12,423	$ 21,982	$ 24,654
Expenses:
Rental property and other expenses	4,573		6,031	9,288	11,698
Depreciation and amortization	2,656		3,110	5,403	6,225
Interest expense	1,342		2,032	2,719	4,181
Total expenses	8,571		11,173	17,410	22,104
Income before disposition of property	2,639		1,250	4,572	2,550
Gains/(losses) on disposition of property	0		16,054	902	18,181
Net income	$ 2,639		$ 17,304	$ 5,474	$ 20,731
Percentage of equity interest in joint ventures, maximum (in hundredths)	50.00%			50.00%
Concourse Center Associates, LLC Joint Venture [Member]
Expenses:
Gains/(losses) on disposition of property		$ (100)
Percentage of equity interest in joint ventures, maximum (in hundredths)		50.00%
Number of buildings sold | property		2
Proceeds received from disposition of property		$ 11,000
Our share of gains on disposition of property		400
Repayment of debt		6,600
4600 Madison Associates, LLC Joint Venture [Member]
Expenses:
Gains/(losses) on disposition of property		$ 1,000
Percentage of equity interest in joint ventures, maximum (in hundredths)		12.50%
Proceeds received from disposition of property		$ 3,400
Our share of gains on disposition of property		100
Repayment of debt		$ 3,400
Fixed current interest rate (in hundredths)		6.85%