Investment in and Advances to Non-Consolidated Entities (Details) (USD $)	9 Months Ended		12 Months Ended	1 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended		12 Months Ended			0 Months Ended	1 Months Ended
	Sep. 30, 2014 sqft	Sep. 30, 2013	Dec. 31, 2012 partnership	Oct. 31, 2013 Joint Venture [Member]	Sep. 30, 2014 Joint Venture [Member]	Dec. 31, 2013 Joint Venture [Member]	Aug. 31, 2013 Baltimore, Maryland [Member] Joint Venture [Member]	Mar. 31, 2013 Palm Beach Gardens, Florida [Member] Joint Venture [Member]	Dec. 31, 2012 Palm Beach Gardens, Florida [Member] Joint Venture [Member] sqft	Dec. 31, 2012 Humble, Texas [Member] Joint Venture [Member]	Dec. 31, 2012 Nonrecourse Mortgage [Member] Humble, Texas [Member] Joint Venture [Member]	Jun. 30, 2014 Office Building [Member] Philadelphia, Pennsylvania [Member] Joint Venture [Member]	Jul. 31, 2014 Office Building [Member] Philadelphia, Pennsylvania [Member] Joint Venture [Member]
Investments in and Advances to Affiliates [Line Items]
Real estate ownership percentage												80.50%	87.50%
Ownership percentage of equity method investment				15.00%				25.00%	36.00%	15.00%
Investment in joint venture	$ 0	$ 5,000,000		$ 39,456,000			$ 5,000,000		$ 29,750,000
Lease term (years)				20 years			99 years		15 years	17 years
Advances to affiliate				18,791,000					12,000,000
Stated interest rate				4.01%							4.70%
Other than temporary impairment on joint venture					930,000	925,000
Number of joint venture formed during period			2
Area of real estate property	1,366,000								120,000
Distributions payable to real estate partnerships								2,557,000
Economic interest in joint venture										100.00%
Property purchase price										27,750,000
Face amount of debt instrument											$ 15,260,000