Investments In Unconsolidated Joint Ventures (Statements Of Operations Of Joint Ventures) (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Schedule of Equity Method Investments [Line Items]
Total revenue (1)	$ 470,904,000		$ 449,703,000		$ 1,389,028,000		$ 1,298,852,000
Expenses
Depreciation and amortization	111,360,000		108,674,000		331,943,000		327,526,000
Total expenses	308,082,000		285,873,000		908,476,000		844,066,000
Operating income	162,822,000		163,830,000		480,552,000		454,786,000
Other expense
Interest expense	105,030,000		95,117,000		308,168,000		288,225,000
Income from continuing operations	66,103,000		80,431,000		219,291,000		198,443,000
Net income	66,103,000		80,451,000		274,859,000		198,383,000
Income from unconsolidated joint ventures	9,217,000		11,326,000		42,129,000		28,184,000
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Total revenue (1)	135,998,000	[1]	150,101,000	[1]	431,133,000	[1]	440,733,000	[1]
Expenses
Operating	42,298,000		44,584,000		120,451,000		129,698,000
Depreciation and amortization	39,291,000		46,773,000		123,869,000		145,653,000
Total expenses	81,589,000		91,357,000		244,320,000		275,351,000
Operating income	54,409,000		58,744,000		186,813,000		165,382,000
Other expense
Interest expense	56,521,000		57,699,000		167,792,000		172,467,000
Impairment loss			39,384,000				39,384,000
Income from continuing operations	(2,112,000)		(38,339,000)		19,021,000		(46,469,000)
Gain on sale of real estate	990,000				990,000
Net income	(1,122,000)		(38,339,000)		20,011,000		(46,469,000)
Company's share of net income (loss)	(1,420,000)		(23,231,000)		10,591,000		(28,570,000)
Basis differential	384,000		25,024,000		1,282,000		28,539,000
Elimination of inter-entity interest on partner loan	10,253,000		9,533,000		30,256,000		28,215,000
Income from unconsolidated joint ventures	9,217,000		11,326,000		42,129,000		28,184,000
Straight-line rent adjustments	2,200,000		6,700,000		9,300,000		14,800,000
"Above" and "below" market rent adjustments, net	22,100,000		28,300,000		70,600,000		87,000,000
Termination income					19,600,000
Company's share of termination income					$ 11,800,000

[1] Includes straight-line rent adjustments of $2.2 million and $6.7 million for the three months ended September 30, 2012 and 2011, respectively, and $9.3 million and $14.8 million for the nine months ended September 30, 2012 and 2011, respectively. Includes net below-market rent adjustments of $22.1 million and $28.3 million for the three months ended September 30, 2012 and 2011, respectively, and $70.6 million and $87.0 million for the nine months ended September 30, 2012 and 2011, respectively. Total revenue for the nine months ended September 30, 2012 includes termination income totaling approximately $19.6 million (of which the Company's share is approximately $11.8 million) related to a lease termination with a tenant at the General Motors Building.