Investment in and Advances to Non-Consolidated Entities (Details) (USD $)	1 Months Ended	9 Months Ended		12 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended			12 Months Ended		12 Months Ended
	Jul. 31, 2012	Sep. 30, 2013 sqft	Sep. 30, 2012	Dec. 31, 2012 Partnerships	Sep. 30, 2013 Joint Venture [Member]	Jun. 30, 2012 Concord and CDH CDO [Member]	Sep. 30, 2013 Concord and CDH CDO [Member]	Aug. 31, 2013 MARYLAND Joint Venture [Member]	Jul. 31, 2013 Long Island City New York [Member] Joint Venture [Member]	Mar. 31, 2013 Palm Beach Garden, FL Office [Member] Joint Venture [Member]	Dec. 31, 2012 Palm Beach Garden, FL Office [Member] Joint Venture [Member] sqft	Sep. 30, 2013 Palm Beach Garden, FL Office [Member] Joint Venture [Member]	Dec. 31, 2012 Humble Texas [Member] Joint Venture [Member]	Dec. 31, 2012 Nonrecourse Mortgage [Member] Humble Texas [Member] Joint Venture [Member]
Investments in and Advances to Affiliates [Line Items]
Investment in joint venture		$ 5,000,000	$ 1,963,000					$ 5,000,000	$ 8,918,000		$ 29,750,000
Lease Term (Years)								99 years			15 years		17 years
Other than temporary impairment on joint venture					925,000
Equity Method Investment, Number of Joint Venture Formed During Period				2
Square Feet		1,442,000									120,000
Equity Method Investment, Ownership Percentage											36.00%	25.00%	15.00%
Advances to Affiliate											12,000,000
Distributions Payable to Real Estate Partnerships										2,557,000
Economic Interest in Joint Venture				100.00%
Property Purchase Price													27,750,000
Debt Instrument, Face Amount														15,260,000
Debt Instrument, Interest Rate, Stated Percentage														4.70%
Proceeds from Divestiture of Interest in Consolidated Subsidiaries	13,218,000
Distributions from joint venture							885,000
Equity Method Investment Sold, Carrying Amount						$ 7,000,000