Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands			3 Months Ended
		Mar. 30, 2021	Mar. 31, 2021		Mar. 31, 2020
Schedule of Equity Method Investments [Line Items]
Total revenue			$ 713,695		$ 752,556
Expenses
Transaction costs			331		615
Depreciation and amortization			176,565		171,094
Total expenses			484,800		481,187
Other income (expense)
Interest expense			(107,902)		(101,591)
Gains on sales of real estate			0		410,165
Net income			128,147		577,146
Income (Loss) from Equity Method Investments			5,225		(369)
Write-off for accrued rent			600		1,200
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]		87,266		93,203
Expenses
Operating			37,134		35,401
Transaction costs			7		0
Depreciation and amortization			34,103		32,035
Total expenses			71,244		67,436
Other income (expense)
Interest expense			(25,556)		(22,583)
Net income			(9,534)		3,184
Company's share of net income			(3,640)		1,252
Gain on Sale of Investments			10,257	[2]	0
Basis differential	[3]		(1,392)		(1,621)
Income (Loss) from Equity Method Investments			5,225		(369)
Straight-line rent adjustments			1,100		9,700
Write-off for accrued rent			300
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments			500		500
Above and below market rent adjustments, net			$ 100		$ 300
540 Madison Avenue [Member]
Other income (expense)
Ownership Percentage	[4]		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%	[5]

[1] Includes straight-line rent adjustments of approximately $1.1 million and $9.7 million for the three months ended March 31, 2021 and 2020, respectively. For the three months ended March 31, 2021, write-offs of accounts receivable and accrued rent balances totaled approximately $0.3 million.

[2] During the three months ended March 31, 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 $0.5 million and $0.5 million for the three months ended March 31, 2021 and 2020, respectively. Also includes net above-/below-market rent adjustments of approximately $0.1 million and $0.3 million for the three months ended March 31, 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 March 31, 2021.

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