Related Party Arrangements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Arrangements
Management, development and other fees	$ 3,572,000	$ 4,147,000	$ 5,599,000
Compensation expense	19,707,000	17,085,000	14,666,000
Unconsolidated real estate entities
Related Party Arrangements
Outstanding receivables	2,519,000	2,449,000
Non-employee directors
Related Party Arrangements
Payable to related parties	90,000
Payable to related parties in quarterly installments	22,500
Non-employee directors | Restricted stock and deferred stock awards
Related Party Arrangements
Payable to related parties	140,000
Compensation expense	1,624,000	1,524,000	1,216,000
Amount of deferred compensation	571,000	$ 525,000	$ 531,000
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
Related Party Arrangements
Payable to related parties	15,000
Payable to related parties in quarterly installments	$ 3,750