Noncontrolling Interests (Property Partnerships) (Narrative) (Details) $ in Thousands			3 Months Ended	9 Months Ended
	Apr. 01, 2019 USD ($)	May 12, 2016 ft²	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Noncontrolling Interest [Line Items]
Noncontrolling Interest in Limited Partnerships			$ 1,720,123	$ 1,720,123		$ 1,711,445
Payments to Noncontrolling Interests				53,149	$ 56,796
Acquisition of noncontrolling interest in property partnerships			43	(186,963)
Salesforce Tower [Member] | Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Portion of project costs covered by a construction loan		50.00%
Portion of costs funded (in percentage)		50.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		5.00%
Debt Instrument, Basis Spread on Variable Rate		3.00%
Stabilization definition for Salesforce Tower		The term stabilization date was defined in the agreement to generally mean the first date after completion upon which Salesforce Tower is (1) at least 90% leased and (2) 50% occupied by tenants that are paying rent.
Net Rentable Area (in sf) | ft²		1,421,000
Salesforce Tower [Member] | Parent Company [Member] | Consolidated Properties [Member]
Noncontrolling Interest [Line Items]
Costs funded (in percentage)		2.50%
Preferred equity funded			$ 22,600	$ 22,600
Salesforce Tower [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	5.00%
Payments to Noncontrolling Interests	$ 210,900
Repayment of Preferred Equity	24,100
Net Payments To Minority Shareholders	$ 186,800
Amount of property owned	100.00%
Acquisition of noncontrolling interest in property partnerships	$ 162,500