Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands			3 Months Ended			6 Months Ended
		Jun. 27, 2019	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018
Schedule of Equity Method Investments [Line Items]
Document Period End Date						Jun. 30, 2019
Total revenue			$ 733,741		$ 664,484	$ 1,459,508		$ 1,325,635
Expenses
Depreciation and amortization			177,411		156,417	342,005		322,214
Total expenses			482,353		433,860	957,944		886,859
Other expense
Interest expense			(102,357)		(92,204)	(203,366)		(182,424)
Gains (loss) on sales of real estate			1,686		18,292	781		114,689
Net income			203,461		160,565	334,620		376,877
Income from unconsolidated joint ventures			47,964		769	48,177		1,230
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]		80,204		57,096	163,159		113,582
Expenses
Operating			30,134		22,868	60,633		45,717
Depreciation and amortization			24,818		14,527	53,464		29,252
Total expenses			54,952		37,395	114,097		74,969
Other expense
Interest expense			(20,803)		(14,708)	(41,560)		(29,132)
Gains (loss) on sales of real estate			34,572	[2]	0	34,572	[2]	0
Net income			39,021		4,993	42,074		9,481
Company's share of net income (loss)			22,376		2,105	23,960		3,931
Basis differential	[2],[3]		25,588		(1,336)	24,217		(2,701)
Income from unconsolidated joint ventures			47,964		769	48,177		1,230
Straight-line rent adjustments			7,600		3,200	13,400		5,000
540 Madison Venture LLC [Member]
Other expense
Equity Method Investment, Realized Gain (Loss) on Disposal		$ 47,800
Colorado Center [Member] | Unconsolidated Joint Ventures [Member]
Other expense
Straight-line rent adjustments			500		700	1,100		1,400
"Above" and "below" market rent adjustments, net			$ 400		$ 400	$ 800		$ 800

[1] Includes straight-line rent adjustments of approximately $7.6 million and $3.2 million for the three months ended June 30, 2019 and 2018, respectively, and $13.4 million and $5.0 million for the six months ended June 30, 2019 and 2018, respectively.

[2] Represents the total gain on sale of 540 Madison Avenue recognized by the joint venture, as described below. During 2008, the Company recognized an other-than-temporary impairment loss on its investment in the unconsolidated joint venture resulting in a basis differential between the carrying value of the Company’s investment in the joint venture and the joint venture’s basis in the assets and liabilities of the property. As a result of the historical basis difference, the Company recognized a gain on sale of real estate totaling approximately $47.8 million, which consists of its share of the gain on sale reported by the joint venture as well as an adjustment for the basis differential. The gain on sale is included in Income from Unconsolidated Joint Ventures in the Company’s Consolidated Statements of Operations.

[3] Includes straight-line rent adjustments of approximately $0.5 million and $0.7 million for the three months ended June 30, 2019 and 2018, respectively, and $1.1 million and $1.4 million for the six months ended June 30, 2019 and 2018, respectively. Also includes net above-/below-market rent adjustments of approximately $0.4 million and $0.4 million for the three months ended June 30, 2019 and 2018, respectively, and $0.8 million and $0.8 million for the six months ended June 30, 2019 and 2018, respectively