Organization and Principles of Consolidation Revenues and Tenant and Other Receivables (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Management, transaction, and other fee [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts Receivable, Net	$ 9,100,000		$ 9,100,000
Parent Company [Member]
Schedule of management, transaction, and other fees [Line Items]
Property Management Fee Revenue	6,887,000	$ 6,601,000	14,045,000	$ 13,307,000
Accounts Receivable, Net	155,540,000		155,540,000		$ 170,985,000
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets					30,903,000
Parent Company [Member] | Property management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Property Management Fee Revenue	3,652,000	3,587,000	7,420,000	7,006,000
Parent Company [Member] | Asset management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Property Management Fee Revenue	1,804,000	1,763,000	3,507,000	3,552,000
Parent Company [Member] | Leasing services [Member]
Schedule of management, transaction, and other fees [Line Items]
Property Management Fee Revenue	1,072,000	787,000	1,757,000	1,617,000
Parent Company [Member] | Other transaction fees [Member]
Schedule of management, transaction, and other fees [Line Items]
Property Management Fee Revenue	359,000	$ 464,000	1,361,000	$ 1,132,000
Parent Company [Member] | Management, transaction, and other fee [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts Receivable, Net					$ 8,700,000
Accounting Standards Update 2017-05 [Member]
Schedule of management, transaction, and other fees [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 30,900,000		$ 30,900,000