Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands			3 Months Ended			6 Months Ended
		Mar. 30, 2021	Jun. 30, 2021		Jun. 30, 2020	Jun. 30, 2021		Jun. 30, 2020	Dec. 31, 2020	[5]
Schedule of Equity Method Investments [Line Items]
Total revenue			$ 713,807		$ 654,773	$ 1,427,502		$ 1,407,329
Expenses
Transaction costs			751		332	1,082		947
Depreciation and amortization			183,838		178,188	360,403		349,282
Total expenses			476,348		460,507	961,148		941,694
Other income (expense)
Interest expense			(106,319)		(107,142)	(214,221)		(208,733)
Gains on sales of real estate			7,756		203,767	7,756		613,932
Net income			141,250		298,580	269,397		875,726
Income (Loss) from Equity Method Investments			(1,373)		1,832	3,852		1,463
Write-off for accrued rent			600		35,900	1,200		37,400
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]		91,226		89,563	178,492		182,766
Expenses
Operating			36,787		33,704	73,921		69,105
Transaction costs			0		0	7		0
Depreciation and amortization			33,627		37,390	67,730		69,425
Total expenses			70,414		71,094	141,658		138,530
Other income (expense)
Interest expense			(25,636)		(23,306)	(51,192)		(45,889)
Gains on sales of real estate					11,720	0		11,720
Net income			(4,824)		6,883	(14,358)		10,067
Company's share of net income			(2,137)		4,024	(5,777)		5,276
Gain on Sale of Investments			0	[2]	0	10,257	[2]	0
Basis differential	[3]		764		(2,192)	(628)		(3,813)
Income (Loss) from Equity Method Investments			(1,373)		1,832	3,852		1,463
Straight-line rent adjustments			5,000		8,500	6,100		18,200
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments			100		400	600		900
Above and below market rent adjustments, net			$ 100		$ 200	$ 200		$ 500
540 Madison Avenue [Member]
Other income (expense)
Ownership Percentage	[4]		60.00%			60.00%
Annapolis Junction NFM, LLC [Member]
Other income (expense)
Gain on Sale of Investments		$ 10,300				$ 10,300
Ownership Percentage		50.00%							50.00%

[1] Includes straight-line rent adjustments of approximately $5.0 million and $8.5 million for the three months ended June 30, 2021 and 2020, respectively, and approximately $6.1 million and $18.2 million for the six months ended June 30, 2021 and 2020, respectively.

[2] During the six months ended June 30, 2021, the Company completed the sale of its 50% ownership interest in Annapolis Junction NFM LLC. The Company recognized a gain on sale of investment of approximately $10.3 million.

[3] Includes straight-line rent adjustments of approximately $0.1 million and $0.4 million for the three months ended June 30, 2021 and 2020, respectively, and approximately $0.6 million and $0.9 million for the six months ended June 30, 2021 and 2020, respectively. Also includes net above-/below-market rent adjustments of approximately $0.1 million and $0.2 million for the three months ended June 30, 2021 and 2020, respectively, and approximately $0.2 million and $0.5 million for the six months ended June 30, 2021 and 2020, respectively.

[4] The property was sold on June 27, 2019. As of December 31, 2020, the investment consisted of undistributed cash. All remaining cash has been distributed as of June 30, 2021.

[5] On March 30, 2021, the Company sold its interest in the joint venture to the partner. See below for additional details.