Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 657,712	$ 625,228	$ 1,946,847	$ 1,914,759
Expenses
Depreciation and amortization		152,164	203,748	463,288	516,371
Total expenses		423,983	467,623	1,268,203	1,288,677
Operating income		233,729	157,605	678,644	626,082
Other expense
Interest expense		92,032	104,641	282,709	314,953
Losses on Extinguishment of Debt		0	371	(14,354)	371
Net income		147,704	71,504	430,278	405,083
Income from unconsolidated joint ventures		843	1,464	7,035	5,489
Mortgage notes payable, net		2,982,067		2,982,067		$ 2,063,087
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	55,516	49,002	166,139	125,039
Expenses
Operating		23,128	21,753	67,310	54,779
Depreciation and amortization		16,440	12,038	44,973	30,306
Total expenses		39,568	33,791	112,283	85,085
Operating income		15,948	15,211	53,856	39,954
Other expense
Interest expense		13,088	8,400	31,815	25,172
Net income		2,860	6,811	22,041	14,782
Company's share of net income		2,909	3,179	11,576	6,830
Basis differential	[2]	(2,066)	(1,715)	(4,541)	(1,341)
Income from unconsolidated joint ventures		843	1,464	7,035	5,489
Straight-line rent adjustments		5,100	5,200	16,400	11,000
Mortgage notes payable, net		1,411,401		1,411,401		$ 865,665
Colorado Center [Member] | Unconsolidated Joint Ventures [Member]
Other expense
Straight-line rent adjustments		700	700	2,200	700
"Above" and "below" market rent adjustments, net		$ 400	$ 500	$ 1,300	$ 500

[1] Includes straight-line rent adjustments of approximately $5.1 million and $5.2 million for the three months ended September 30, 2017 and 2016, respectively, and $16.4 million and $11.0 million for the nine months ended September 30, 2017 and 2016, respectively.

[2] Includes straight-line rent adjustments of approximately $0.7 million and $0.7 million for the three months ended September 30, 2017 and 2016, respectively, and $2.2 million and $0.7 million for the nine months ended September 30, 2017 and 2016, respectively. Also includes net above-/below-market rent adjustments of approximately $0.4 million and $0.5 million for the three months ended September 30, 2017 and 2016, respectively, and $1.3 million and $0.5 million for the nine months ended September 30, 2017 and 2016, respectively.