Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
ASSETS
Land and improvements	$ 1,234,013	$ 1,202,872
Buildings and tenant improvements	4,925,527	4,766,793
Construction in progress	165,893	44,259
Investments in and advances to unconsolidated companies	368,000	364,859
Undeveloped land	622,457	622,635
Real estate investment property, at cost, total	7,315,890	7,001,418
Accumulated depreciation	(1,199,073)	(1,108,650)
Net real estate investments	6,116,817	5,892,768
Real estate investments and other assets held-for-sale	11,733	55,580
Cash and cash equivalents	106,565	213,809
Accounts receivable, net of allowance of $2,753 and $3,597	19,618	22,255
Straight-line rent receivable, net of allowance of $6,565 and $7,447	112,255	105,900
Receivables on construction contracts, including retentions	32,969	40,247
Deferred financing costs, net of accumulated amortization of $45,667 and $59,109	41,231	42,268
Deferred leasing and other costs, net of accumulated amortization of $337,543 and $292,334	460,079	460,881
Escrow deposits and other assets	166,823	170,729
Total Assets	7,068,090	7,004,437
LIABILITIES AND EQUITY
Secured debt	1,101,195	1,173,233
Unsecured notes	2,915,155	2,616,063
Unsecured lines of credit	20,293	20,293
Long-term debt, total	4,036,643	3,809,589
Liabilities related to real estate investments held-for-sale	379	975
Construction payables and amounts due subcontractors, including retentions	60,931	55,775
Accrued real estate taxes	85,779	69,272
Accrued interest	59,506	58,904
Other accrued expenses	37,506	60,174
Other liabilities	125,890	131,735
Tenant security deposits and prepaid rents	42,078	38,355
Total Liabilities	4,448,712	4,224,779
Equity
Preferred shares ($.01 par value); 5,000 shares authorized; 2,503 and 3,176 shares issued and outstanding	625,638	793,910
Common shares ($.01 par value); 400,000 shares authorized; 267,523 and 252,927 shares issued and outstanding	2,675	2,529
Additional paid-in capital	3,783,746	3,594,588
Accumulated other comprehensive income	1,767	987
Distributions in excess of net income	(1,833,088)	(1,677,328)
Total shareholders' equity	2,580,738	2,714,686
Noncontrolling interests	38,640	64,972
Total Equity	2,619,378	2,779,658
Total Liabilities and Equity	7,068,090	7,004,437
Subsidiary of Common Parent [Member]
ASSETS
Land and improvements	1,234,013	1,202,872
Buildings and tenant improvements	4,925,527	4,766,793
Construction in progress	165,893	44,259
Investments in and advances to unconsolidated companies	368,000	364,859
Undeveloped land	622,457	622,635
Real estate investment property, at cost, total	7,315,890	7,001,418
Accumulated depreciation	(1,199,073)	(1,108,650)
Net real estate investments	6,116,817	5,892,768
Real estate investments and other assets held-for-sale	11,733	55,580
Cash and cash equivalents	106,565	213,826
Accounts receivable, net of allowance of $2,753 and $3,597	19,618	22,255
Straight-line rent receivable, net of allowance of $6,565 and $7,447	112,255	105,900
Receivables on construction contracts, including retentions	32,969	40,247
Deferred financing costs, net of accumulated amortization of $45,667 and $59,109	41,231	42,268
Deferred leasing and other costs, net of accumulated amortization of $337,543 and $292,334	460,079	460,881
Escrow deposits and other assets	166,823	170,257
Total Assets	7,068,090	7,003,982
LIABILITIES AND EQUITY
Secured debt	1,101,195	1,173,233
Unsecured notes	2,915,155	2,616,063
Unsecured lines of credit	20,293	20,293
Long-term debt, total	4,036,643	3,809,589
Liabilities related to real estate investments held-for-sale	379	975
Construction payables and amounts due subcontractors, including retentions	60,931	55,775
Accrued real estate taxes	85,779	69,272
Accrued interest	59,506	58,904
Other accrued expenses	37,598	59,795
Other liabilities	125,890	131,735
Tenant security deposits and prepaid rents	42,078	38,355
Total Liabilities	4,448,804	4,224,400
Equity
Common equity (267,523 and 252,927 General Partner Units issued and outstanding)	1,957,414	1,923,886
Preferred equity (2,503 and 3,176 Preferred Units issued and outstanding)	625,638	793,910
General Partners' equity	2,583,052	2,717,796
Limited Partners' common equity (4,511 and 6,945 Limited Partner Units issued and outstanding)	24,213	56,254
Accumulated other comprehensive income	1,767	987
Total partners' equity	2,609,032	2,775,037
Noncontrolling interests	10,254	4,545
Total Equity	2,619,286	2,779,582
Total Liabilities and Equity	$ 7,068,090	$ 7,003,982