Related Party Arrangements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Arrangements
Management, development and other fees	$ 3,819,000	$ 4,960,000	$ 3,572,000
Compensation expense	21,110,000	24,885,000	19,707,000
Unconsolidated Real Estate Entities [Member]
Related Party Arrangements
Outstanding receivables	5,408,000	3,924,000
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	170,000
Compensation expense	1,819,000	1,725,000	1,624,000
Amount of deferred compensation	614,000	$ 594,000	$ 571,000
Lead Independent Director
Related Party Arrangements
Payable to related parties	30,000
Payable to related parties in quarterly installments	7,500
Non Employee Director Serving As A Chairperson of the Audit Committee [Member]
Related Party Arrangements
Payable to related parties	25,000
Payable to related parties in quarterly installments	6,250
Non Employee Director Serving As A Chairperson of the Compensation Committee [Member]
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