Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
ASSETS
Land and improvements	$ 1,278,428	$ 1,284,081
Buildings and tenant improvements	5,326,997	5,398,886
Construction in progress	303,383	234,918
Investments in and advances to unconsolidated companies	331,041	372,256
Undeveloped land	607,283	614,208
Real estate investment property, at cost, total	7,847,132	7,904,349
Accumulated depreciation	(1,319,056)	(1,296,396)
Net real estate investments	6,528,076	6,607,953
Real estate investments and other assets held-for-sale	105,505	30,937
Cash and cash equivalents	307,167	33,889
Accounts receivable, net of allowance	21,175	22,283
Straight-line rent receivable, net of allowance	121,457	120,303
Receivables on construction contracts, including retentions	27,465	39,754
Deferred financing costs, net of accumulated amortization	41,097	40,083
Deferred leasing and other costs, net of accumulated amortization	480,458	497,827
Escrow deposits and other assets	169,699	167,072
Total Assets	7,802,099	7,560,101
LIABILITIES AND EQUITY
Secured debt	1,151,660	1,167,953
Unsecured notes	3,242,737	2,993,217
Unsecured line of credit	0	285,000
Long-term debt, total	4,394,397	4,446,170
Liabilities related to real estate investments held-for-sale	1,973	807
Construction payables and amounts due subcontractors, including retentions	81,044	84,679
Accrued real estate taxes	78,524	74,565
Accrued interest	41,626	59,215
Other accrued expenses	33,056	57,881
Other liabilities	123,233	167,935
Tenant security deposits and prepaid rents	43,665	42,731
Total Liabilities	4,797,518	4,933,983
Equity
Preferred shares	447,683	625,638
Common shares	3,217	2,794
Additional paid-in capital	4,536,904	3,953,497
Accumulated other comprehensive income	3,228	2,691
Distributions in excess of net income	(2,020,455)	(1,993,206)
Total shareholders' equity	2,970,577	2,591,414
Noncontrolling interests	34,004	34,704
Total Equity	3,004,581	2,626,118
Total Liabilities and Equity	7,802,099	7,560,101
Subsidiary of Common Parent [Member]
ASSETS
Land and improvements	1,278,428	1,284,081
Buildings and tenant improvements	5,326,997	5,398,886
Construction in progress	303,383	234,918
Investments in and advances to unconsolidated companies	331,041	372,256
Undeveloped land	607,283	614,208
Real estate investment property, at cost, total	7,847,132	7,904,349
Accumulated depreciation	(1,319,056)	(1,296,396)
Net real estate investments	6,528,076	6,607,953
Real estate investments and other assets held-for-sale	105,505	30,937
Cash and cash equivalents	307,167	33,889
Accounts receivable, net of allowance	21,175	22,283
Straight-line rent receivable, net of allowance	121,457	120,303
Receivables on construction contracts, including retentions	27,465	39,754
Deferred financing costs, net of accumulated amortization	41,097	40,083
Deferred leasing and other costs, net of accumulated amortization	480,458	497,827
Escrow deposits and other assets	169,699	167,072
Total Assets	7,802,099	7,560,101
LIABILITIES AND EQUITY
Secured debt	1,151,660	1,167,953
Unsecured notes	3,242,737	2,993,217
Unsecured line of credit	0	285,000
Long-term debt, total	4,394,397	4,446,170
Liabilities related to real estate investments held-for-sale	1,973	807
Construction payables and amounts due subcontractors, including retentions	81,044	84,679
Accrued real estate taxes	78,524	74,565
Accrued interest	41,626	59,215
Other accrued expenses	33,252	58,048
Other liabilities	123,233	167,935
Tenant security deposits and prepaid rents	43,665	42,731
Total Liabilities	4,797,714	4,934,150
Equity
Common equity	2,523,643	1,967,091
Preferred equity	447,683	625,638
General Partners' equity	2,971,326	2,592,729
Limited Partners' common equity	20,687	21,383
Accumulated other comprehensive income	3,228	2,691
Total partners' equity	2,995,241	2,616,803
Noncontrolling interests	9,144	9,148
Total Equity	3,004,385	2,625,951
Total Liabilities and Equity	$ 7,802,099	$ 7,560,101