Related Party Arrangements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Arrangements
Management fees revenue	$ 4,147,000	$ 5,599,000	$ 9,947,000
Compensation expense	17,085,000	14,666,000	14,703,000
Unconsolidated real estate entities
Related Party Arrangements
Outstanding receivables	2,449,000	5,239,000
Non-employee directors
Related Party Arrangements
Payable to related parties	80,000
Payable to related parties in quarterly installments	20,000
Non-employee directors | Restricted stock and deferred stock awards
Related Party Arrangements
Payable to related parties	135,000
Compensation expense	1,524,000	1,216,000	1,135,000
Amount of deferred compensation	525,000	$ 531,000	$ 488,000
Lead Independent Director
Related Party Arrangements
Payable to related parties	30,000
Payable to related parties in quarterly installments	7,500
Non-employees directors serving as a chairperson
Related Party Arrangements
Payable to related parties	20,000
Payable to related parties in quarterly installments	5,000
Non Employee Director Serving As A Chairperson of the Nominating and Corporate Governance or Investment and Finance Committees [Member]
Related Party Arrangements
Payable to related parties	15,000
Payable to related parties in quarterly installments	$ 3,750