Organization and Significant Accounting Policies - Revenues and Tenant and Other Receivables (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule of management, transaction, and other fees [Line Items]
Other property income	$ 2,261	$ 2,780	$ 7,001	$ 6,956
Management, transaction, and other fees	6,142	7,353	19,084	21,768
Tenant and other receivables	159,137		159,137		$ 169,337
Management, transaction, and other fee [Member]
Schedule of management, transaction, and other fees [Line Items]
Tenant and other receivables	9,800		9,800		$ 11,600
Property management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	3,598	3,648	10,830	11,076
Asset management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	1,657	1,803	5,250	5,341
Leasing services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	708	1,239	1,948	2,702
Other transaction fees [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	$ 179	$ 663	$ 1,056	$ 2,649