Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 693,268	$ 743,553	$ 2,100,597	$ 2,203,061
Expenses
Transaction costs		307	538	1,254	1,415
Depreciation and amortization		166,456	165,862	515,738	507,867
Total expenses		458,946	474,322	1,400,640	1,432,266
Other income (expense)
Interest expense		(110,993)	(106,471)	(319,726)	(309,837)
Gains on sales of real estate		(209)	(15)	613,723	766
Net income		118,060	141,370	993,786	475,990
Income (loss) from unconsolidated joint ventures		(6,873)	(649)	(5,410)	47,528
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	87,724	75,940	270,490	239,099
Expenses
Operating		37,572	28,839	106,677	89,472
Depreciation and amortization		35,810	23,477	105,235	76,941
Total expenses		73,382	52,316	211,912	166,413
Other income (expense)
Interest expense		(25,481)	(20,483)	(71,370)	(62,043)
Gains on sales of real estate		0	(812)	11,720	33,760
Net income		(11,139)	2,329	(1,072)	44,403
Company's share of net income		(4,421)	392	855	24,352
Basis differential	[2]	(2,452)	(1,041)	(6,265)	23,176
Income (loss) from unconsolidated joint ventures		(6,873)	(649)	(5,410)	47,528
Straight-line rent adjustments		3,800	5,300	22,000	18,700
Colorado Center [Member]
Other income (expense)
Straight-line rent adjustments		400	500	1,300	1,600
Above and below market rent adjustments, net		$ 200	$ 400	$ 700	$ 1,300

[1] Includes straight-line rent adjustments of approximately $3.8 million and $5.3 million for the three months ended September 30, 2020 and 2019, respectively, and $22.0 million and $18.7 million for the nine months ended September 30, 2020 and 2019, respectively.

[2] Includes straight-line rent adjustments of approximately $0.4 million and $0.5 million for the three months ended September 30, 2020 and 2019, respectively, and $1.3 million and $1.6 million for the nine months ended September 30, 2020 and 2019, respectively. Also includes net above-/below-market rent adjustments of approximately $0.2 million and $0.4 million for the three months ended September 30, 2020 and 2019, respectively, and $0.7 million and $1.3 million for the nine months ended September 30, 2020 and 2019, respectively.