Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets [Abstract]
Land and improvements	$ 1,284,081	$ 1,202,872
Building and tenant Improvements	5,398,886	4,766,793
Construction in Progress	234,918	44,259
Investments in and advances to unconsolidated companies	372,256	364,859
Undeveloped land	614,208	622,635
Real estate investment property, at cost, total	7,904,349	7,001,418
Accumulated depreciation	(1,296,396)	(1,108,650)
Net real estate investments	6,607,953	5,892,768
Real estate investments and other assets held-for-sale	30,937	55,580
Cash and cash equivalents	33,889	213,809
Accounts receivable, net of allowance	22,283	22,255
Straight-line rent receivable, net of allowance	120,303	105,900
Receivables on construction contracts, including retentions	39,754	40,247
Deferred financing costs, net of accumulated amortization	40,083	42,268
Deferred leasing and other costs, net of accumulated amortization	497,827	460,881
Escrow deposits and other assets	167,072	170,729
Total Assets	7,560,101	7,004,437
Liabilities and Equity [Abstract]
Secured Debt	1,167,953	1,173,233
Unsecured notes	2,993,217	2,616,063
Unsecured lines of credit	285,000	20,293
Long-term debt, total	4,446,170	3,809,589
Liabilities related to real estate investments held-for-sale	807	975
Construction payables and amounts due subcontractors, including retentions	84,679	55,775
Accrued real estate taxes	74,565	69,272
Accrued interest	59,215	58,904
Other accrued expenses	57,881	60,174
Other Liabilities	167,935	131,735
Tenant security deposits and prepaid rents	42,731	38,355
Total Liabilities	4,933,983	4,224,779
Equity:
Preferred Shares	625,638	793,910
Common shares	2,794	2,529
Additional paid in capital	3,953,497	3,594,588
Accumulated other comprehensive income (loss)	2,691	987
Distributions in excess of net income	(1,993,206)	(1,677,328)
Total stockholders' equity	2,591,414	2,714,686
Noncontrolling interests	34,704	64,972
Total Equity	2,626,118	2,779,658
Total Liabilities and Equity	7,560,101	7,004,437
Subsidiary of Common Parent [Member]
Assets [Abstract]
Land and improvements	1,284,081	1,202,872
Building and tenant Improvements	5,398,886	4,766,793
Construction in Progress	234,918	44,259
Investments in and advances to unconsolidated companies	372,256	364,859
Undeveloped land	614,208	622,635
Real estate investment property, at cost, total	7,904,349	7,001,418
Accumulated depreciation	(1,296,396)	(1,108,650)
Net real estate investments	6,607,953	5,892,768
Real estate investments and other assets held-for-sale	30,937	55,580
Cash and cash equivalents	33,889	213,826
Accounts receivable, net of allowance	22,283	22,255
Straight-line rent receivable, net of allowance	120,303	105,900
Receivables on construction contracts, including retentions	39,754	40,247
Deferred financing costs, net of accumulated amortization	40,083	42,268
Deferred leasing and other costs, net of accumulated amortization	497,827	460,881
Escrow deposits and other assets	167,072	170,257
Total Assets	7,560,101	7,003,982
Liabilities and Equity [Abstract]
Secured Debt	1,167,953	1,173,233
Unsecured notes	2,993,217	2,616,063
Unsecured lines of credit	285,000	20,293
Long-term debt, total	4,446,170	3,809,589
Liabilities related to real estate investments held-for-sale	807	975
Construction payables and amounts due subcontractors, including retentions	84,679	55,775
Accrued real estate taxes	74,565	69,272
Accrued interest	59,215	58,904
Other accrued expenses	58,048	59,795
Other Liabilities	167,935	131,735
Tenant security deposits and prepaid rents	42,731	38,355
Total Liabilities	4,934,150	4,224,400
Equity:
Common equity	1,967,091	1,923,886
Preferred equity	625,638	793,910
General Partners' equity	2,592,729	2,717,796
Limited Partners' common equity	21,383	56,254
Accumulated other comprehensive income (loss)	2,691	987
Total partners' equity	2,616,803	2,775,037
Noncontrolling interest	9,148	4,545
Total Equity	2,625,951	2,779,582
Total Liabilities and Equity	$ 7,560,101	$ 7,003,982