Summary of Significant Accounting Policies Revenues and Tenant and Other Receivables (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2020 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees		$ 26,501	$ 29,636	$ 28,494
Tenant and other receivables		143,633	169,337
Lease liabilities		220,390	222,918		$ 225,400
Right of use assets, net		287,827	292,786		$ 297,800
Management, transaction, and other fee [Member]
Schedule of management, transaction, and other fees [Line Items]
Tenant and other receivables		9,900	11,600
Property management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees		14,444	14,744	14,663
Asset management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees		6,963	7,135	7,213
Leasing services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees		3,150	3,692	4,044
Other transaction fees [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees		1,944	4,065	2,574
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
Tenant Receivables [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net		39,658	35,526
Straight-line Rent Receivables [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net		86,615	107,087
Other Receivable [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net	[1]	17,360	26,724
Parent Company [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net		$ 143,633	$ 169,337
COVID-19 [Member]
Schedule of management, transaction, and other fees [Line Items]
Number of rent deferrals		1,600
Deferred rent period		3.3 months
Deferred rent repayment period		9.7 months
Deferred rent receivables		$ 40,800
Deferred rent on pro rata		4.6
Leases less than 10,000 sqft [Member]
Schedule of management, transaction, and other fees [Line Items]
Operating leases, tenant space terms | ft²		10,000
Leases greater then 10,000 sqft [Member]
Schedule of management, transaction, and other fees [Line Items]
Operating leases, tenant space terms | ft²		10,000
Minimum [Member]
Schedule of management, transaction, and other fees [Line Items]
Operating leases, lease year range		3 years
Operating leases, lease year range for tenant space greater than 10,000 sq ft		5 years
Maximum [Member]
Schedule of management, transaction, and other fees [Line Items]
Operating leases, lease year range		7 years

[1] Other receivables include construction receivables, insurance receivables, and amounts due from real estate partnerships for Management, transaction and other fee income.