Investments in Unconsolidated Joint Ventures (Statements of Operations of the Joint Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Total revenue		$ 725,767	$ 661,151
Expenses
Depreciation and amortization		164,594	165,797
Total expenses		475,591	452,999
Other expense
Interest expense		101,009	90,220
Net income		131,159	216,312
Income from unconsolidated joint ventures		213	461
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue	[1]	82,955	56,486
Expenses
Operating		30,499	22,849
Depreciation and amortization		28,646	14,725
Total expenses		59,145	37,574
Other expense
Interest expense		20,757	14,424
Net income		3,053	4,488
Company's share of net income (loss)		1,584	1,826
Basis differential	[2]	(1,371)	(1,365)
Income from unconsolidated joint ventures		213	461
Straight-line rent adjustments		5,800	1,800
Colorado Center [Member] | Unconsolidated Joint Ventures [Member]
Other expense
Straight-line rent adjustments		500	700
"Above" and "below" market rent adjustments, net		$ 400	$ 400

[1] Includes straight-line rent adjustments of approximately $5.8 million and $1.8 million for the three months ended March 31, 2019 and 2018, respectively

[2] Includes straight-line rent adjustments of approximately $0.5 million and $0.7 million for the three months ended March 31, 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 March 31, 2019 and 2018, respectively