Real Estate (Schedule Of Allocation Of The Aggregate Purchase Price Of Acquisition) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 10, 2013	May 31, 2013
Restructuring Cost and Reserve [Line Items]
Real estate and related intangibles recorded upon consolidation	$ 0	$ 3,356,000	$ 0
Mortgage notes payable	(4,309,484)	(4,449,734)
Mezzanine notes payable	(309,796)	(311,040)
Outside members' notes payable	(180,000)	(180,000)
Debt recorded upon consolidation	0	(2,056,000)	0
Cash and cash equivalents	0	79,468	0
Accrued interest payable	(163,532)	(167,523)
Working capital recorded upon consolidation	0	(177,315)	0
Noncontrolling interest in property partnerships recorded upon consolidation	0	(480,861)	0
Mountain View Research And Technology Parks [Member]
Restructuring Cost and Reserve [Line Items]
Land				126,521
Building and improvements				82,451
Tenant Improvements				7,326
In-place lease Intangibles				23,279
Above market rents				843
Below market rents				(7,336)
Aggregate purchase price				233,084
767 5th Avenue (The General Motors Building) [Member]
Restructuring Cost and Reserve [Line Items]
Land					1,796,252
Building and improvements					1,447,446
Tenant Improvements					85,208
In-place lease Intangibles					357,781
Above market rents					101,897
Below market rents					(239,641)
Above Market Assumed Debt Adjustments					(192,943)
Real estate and related intangibles recorded upon consolidation					3,356,000
Mortgage notes payable					(1,300,000)
Mezzanine notes payable					(306,000)
Outside members' notes payable					(450,000)	[1]
Debt recorded upon consolidation					(2,056,000)
Cash and cash equivalents					79,468
Cash held in escrows					2,403
Tenant and other receivables					7,104
Prepaid expenses and other assets					4,269
Accounts payable and other expenses					(2,418)
Accrued interest payable					(182,369)	[2]
Other liabilities					6,304
Working capital recorded upon consolidation					(97,847)
Noncontrolling Interest					(520,000)
Noncontrolling Interest working capital					39,139
Noncontrolling interest in property partnerships recorded upon consolidation					(480,861)
Net Assets Recorded Upon Consolidation					721,292
Consolidation, Eliminations [Member] | 767 5th Avenue (The General Motors Building) [Member]
Restructuring Cost and Reserve [Line Items]
Outside members' notes payable					(270,000)
Accrued interest payable					$ (105,500)

[1] (1)The Company's member loan totaling $270.0 million eliminates in consolidation.

[2] (2)The Company's share of the accrued interest payable on the members' loans totaling approximately $105.5 million eliminates in consolidation.