Subsequent Events Narrative (Details) ft² in Thousands, $ in Thousands				3 Months Ended
		Apr. 26, 2019 USD ($) ft² yr	Apr. 01, 2019 USD ($) ft²	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Apr. 18, 2019 USD ($) ft²
Subsequent Event [Line Items]
Payments to Noncontrolling Interests				$ 24,128	$ 30,690
Salesforce Tower [Member]
Subsequent Event [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners			5.00%
Payments to Noncontrolling Interests			$ 210,900
Repayment of Preferred Equity			$ 24,100
7750 Wisconsin Avenue LLC [Member]
Subsequent Event [Line Items]
Ownership Percentage	[1]			50.00%
Subsequent Event [Member] | Salesforce Tower [Member]
Subsequent Event [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners			5.00%
Payments to Noncontrolling Interests			$ 210,900
Repayment of Preferred Equity			$ 24,100
Net Rentable Area (in sf) | ft²			1,421
Subsequent Event [Member] | One Tower Center [Member]
Subsequent Event [Line Items]
Net Rentable Area (in sf) | ft²						410
Gross Sale Price						$ 38,000
Subsequent Event [Member] | 7750 Wisconsin Avenue LLC [Member]
Subsequent Event [Line Items]
Net Rentable Area (in sf) | ft²		734
Ownership Percentage		50.00%
Construction Loan Facility Borrowing Capacity		$ 255,000
Debt Instrument, Basis Spread on Variable Rate		1.25%
Number of extensions		2
Extension Option (in years) | yr		1

[1] This entity is a VIE (See Note 2).