Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 656,907	$ 623,546	$ 1,289,135	$ 1,289,531
Expenses
Depreciation and amortization		151,919	153,175	311,124	312,623
Total expenses		418,217	405,422	844,220	821,054
Operating income		238,690	218,124	444,915	468,477
Other expense
Interest expense		95,143	105,003	190,677	210,312
Losses on Extinguishment of Debt		(14,354)	0	(14,354)	0
Net income		167,010	117,357	282,574	333,579
Income from unconsolidated joint ventures		3,108	2,234	6,192	4,025
Mortgage notes payable, net		2,986,283		2,986,283		$ 2,063,087
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	55,862	38,368	110,623	76,037
Expenses
Operating		22,103	16,359	44,182	33,026
Depreciation and amortization		14,224	9,204	28,533	18,268
Total expenses		36,327	25,563	72,715	51,294
Operating income		19,535	12,805	37,908	24,743
Other expense
Interest expense		9,427	8,383	18,727	16,772
Net income		10,108	4,422	19,181	7,971
Company's share of net income		4,344	2,052	8,667	3,651
Basis differential	[2]	(1,236)	182	(2,475)	374
Income from unconsolidated joint ventures		3,108	2,234	6,192	4,025
Straight-line rent adjustments		4,300	$ 3,600	11,300	$ 5,800
Mortgage notes payable, net		863,981		863,981		$ 865,665
Colorado Center [Member] | Unconsolidated Joint Ventures [Member]
Other expense
Straight-line rent adjustments		800		1,500
"Above" and "below" market rent adjustments, net		$ 400		$ 900

[1] Includes straight-line rent adjustments of approximately $4.3 million and $3.6 million for the three months ended June 30, 2017 and 2016, respectively and $11.3 million and $5.8 million for the six months ended June 30, 2017 and 2016, respectively.

[2] Includes straight-line rent adjustments of approximately $0.8 million and $1.5 million for the three and six months ended June 30, 2017, respectively, and net above-/below-market rent adjustments of approximately $0.4 million and $0.9 million for the three and six months ended June 30, 2017, respectively.