Summary of Significant Accounting Policies Revenues and Tenant and Other Receivables (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Schedule of management, transaction, and other fees [Line Items]
Accrued CAM, insurance and tax reimbursements	$ 10,620	$ 25,305
Straight-line rent receivables	107,087	105,677
Provision for Doubtful Accounts		(10,100)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets			$ 30,903
Other property income	9,201	8,711	7,982
Management, transaction, and other fees	29,636	28,494	26,158
Tenant and other receivables (note 1)	169,337	172,359
Lease liabilities	222,918	0		$ 225,400
Right of use assets, net	292,786	0		$ 297,800
Management, transaction, and other fee [Member]
Schedule of management, transaction, and other fees [Line Items]
Tenant and other receivables (note 1)	11,600	12,500
Property management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	14,744	14,663	13,917
Asset management services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	7,135	7,213	7,090
Leasing services [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	3,692	4,044	3,573
Other transaction fees [Member]
Schedule of management, transaction, and other fees [Line Items]
Management, transaction, and other fees	4,065	2,574	$ 1,578
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
Parent Company [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net	169,337	172,359
Billed Tenant Receivables [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net	24,906	25,590
Other Receivable [Member]
Schedule of management, transaction, and other fees [Line Items]
Accounts and Notes Receivable, Net	$ 26,724	30,953
straight line rent [Member]
Schedule of management, transaction, and other fees [Line Items]
Provision for Doubtful Accounts		$ (5,066)
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