Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
ASSETS
Land and improvements	$ 1,239,276	$ 1,202,872
Buildings and tenant improvements	5,016,464	4,766,793
Construction in progress	219,931	44,259
Investments in and advances to unconsolidated companies	367,221	364,859
Undeveloped land	613,183	622,635
Real estate investment property, at cost, total	7,456,075	7,001,418
Accumulated depreciation	(1,246,853)	(1,108,650)
Net real estate investments	6,209,222	5,892,768
Real estate investments and other assets held-for-sale	0	55,580
Cash and cash equivalents	113,152	213,809
Accounts receivable, net of allowance of $3,080 and $3,597	29,737	22,255
Straight-line rent receivable, net of allowance of $5,274 and $7,447	117,016	105,900
Receivables on construction contracts, including retentions	36,413	40,247
Deferred financing costs, net of accumulated amortization of $45,233 and $59,109	42,095	42,268
Deferred leasing and other costs, net of accumulated amortization of $356,776 and $292,334	465,588	460,881
Escrow deposits and other assets	176,894	170,729
Total Assets	7,190,117	7,004,437
LIABILITIES AND EQUITY
Secured debt	1,096,455	1,173,233
Unsecured notes	3,043,690	2,616,063
Unsecured lines of credit	0	20,293
Long-term debt, total	4,140,145	3,809,589
Liabilities related to real estate investments held-for-sale	0	975
Construction payables and amounts due subcontractors, including retentions	80,934	55,775
Accrued real estate taxes	102,646	69,272
Accrued interest	36,666	58,904
Other accrued expenses	41,661	60,174
Other liabilities	122,776	131,735
Tenant security deposits and prepaid rents	40,248	38,355
Total Liabilities	4,565,076	4,224,779
Equity
Preferred shares ($.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; 273,519 and 252,927 shares issued and outstanding	2,735	2,529
Additional paid-in capital	3,871,155	3,594,588
Accumulated other comprehensive income	2,177	987
Distributions in excess of net income	(1,912,802)	(1,677,328)
Total shareholders' equity	2,588,903	2,714,686
Noncontrolling interests	36,138	64,972
Total Equity	2,625,041	2,779,658
Total Liabilities and Equity	7,190,117	7,004,437
Subsidiary of Common Parent [Member]
ASSETS
Land and improvements	1,239,276	1,202,872
Buildings and tenant improvements	5,016,464	4,766,793
Construction in progress	219,931	44,259
Investments in and advances to unconsolidated companies	367,221	364,859
Undeveloped land	613,183	622,635
Real estate investment property, at cost, total	7,456,075	7,001,418
Accumulated depreciation	(1,246,853)	(1,108,650)
Net real estate investments	6,209,222	5,892,768
Real estate investments and other assets held-for-sale	0	55,580
Cash and cash equivalents	113,152	213,826
Accounts receivable, net of allowance of $3,080 and $3,597	29,737	22,255
Straight-line rent receivable, net of allowance of $5,274 and $7,447	117,016	105,900
Receivables on construction contracts, including retentions	36,413	40,247
Deferred financing costs, net of accumulated amortization of $45,233 and $59,109	42,095	42,268
Deferred leasing and other costs, net of accumulated amortization of $356,776 and $292,334	465,588	460,881
Escrow deposits and other assets	176,894	170,257
Total Assets	7,190,117	7,003,982
LIABILITIES AND EQUITY
Secured debt	1,096,455	1,173,233
Unsecured notes	3,043,690	2,616,063
Unsecured lines of credit	0	20,293
Long-term debt, total	4,140,145	3,809,589
Liabilities related to real estate investments held-for-sale	0	975
Construction payables and amounts due subcontractors, including retentions	80,934	55,775
Accrued real estate taxes	102,646	69,272
Accrued interest	36,666	58,904
Other accrued expenses	41,768	59,795
Other liabilities	122,776	131,735
Tenant security deposits and prepaid rents	40,248	38,355
Total Liabilities	4,565,183	4,224,400
Equity
Common equity (273,519 and 252,927 General Partner Units issued and outstanding)	1,965,154	1,923,886
Preferred equity (2,503 and 3,176 Preferred Units issued and outstanding)	625,638	793,910
General Partners' equity	2,590,792	2,717,796
Limited Partners' common equity (4,511 and 6,945 Limited Partner Units issued and outstanding)	22,993	56,254
Accumulated other comprehensive income	2,177	987
Total partners' equity	2,615,962	2,775,037
Noncontrolling interests	8,972	4,545
Total Equity	2,624,934	2,779,582
Total Liabilities and Equity	$ 7,190,117	$ 7,003,982