Related Party Transactions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amounts due from/to related parties
Due from joint ventures	$ 1,254,000	$ 2,376,000
Other	10,481,000	6,154,000
Related party receivables	11,735,000	8,530,000
Alliance Building Services
Related Party Transactions
Profit participation from related party	3,800,000	3,500,000	4,000,000
Payments made for services	21,500,000	23,400,000	20,500,000
Entity with Stephen L Green ownership interest
Related Party Transactions
Property management fees from related party	$ 444,300	$ 441,100	$ 384,900