Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
ASSETS
Land and improvements	$ 1,406,083	$ 1,284,081
Buildings and tenant improvements	5,651,157	5,398,886
Construction in progress	266,362	234,918
Investments in and advances to unconsolidated companies	327,698	372,256
Undeveloped land	599,214	614,208
Real estate investment property, at cost, total	8,250,514	7,904,349
Accumulated depreciation	(1,359,389)	(1,296,396)
Net real estate investments	6,891,125	6,607,953
Real estate investments and other assets held-for-sale	57,046	30,937
Cash and cash equivalents	21,402	33,889
Accounts receivable, net of allowance	21,073	22,283
Straight-line rent receivable, net of allowance	124,058	120,303
Receivables on construction contracts, including retentions	30,205	39,754
Deferred financing costs, net of accumulated amortization	40,837	40,083
Deferred leasing and other costs, net of accumulated amortization	521,673	497,827
Escrow deposits and other assets	176,483	167,072
Total Assets	7,883,902	7,560,101
LIABILITIES AND EQUITY
Secured debt	1,241,527	1,167,953
Unsecured debt	3,067,250	2,993,217
Unsecured line of credit	88,000	285,000
Long-term debt, total	4,396,777	4,446,170
Liabilities related to real estate investments held-for-sale	749	807
Construction payables and amounts due subcontractors, including retentions	87,730	84,679
Accrued real estate taxes	86,528	74,565
Accrued interest	58,426	59,215
Other accrued expenses	44,822	104,719
Other liabilities	123,649	121,097
Tenant security deposits and prepaid rents	42,755	42,731
Total Liabilities	4,841,436	4,933,983
Equity
Preferred shares	447,683	625,638
Common shares	3,233	2,794
Additional paid-in capital	4,567,898	3,953,497
Accumulated other comprehensive income	3,950	2,691
Distributions in excess of net income	(2,014,399)	(1,993,206)
Total shareholders' equity	3,008,365	2,591,414
Noncontrolling interests	34,101	34,704
Total Equity	3,042,466	2,626,118
Total Liabilities and Equity	7,883,902	7,560,101
Subsidiary of Common Parent [Member]
ASSETS
Land and improvements	1,406,083	1,284,081
Buildings and tenant improvements	5,651,157	5,398,886
Construction in progress	266,362	234,918
Investments in and advances to unconsolidated companies	327,698	372,256
Undeveloped land	599,214	614,208
Real estate investment property, at cost, total	8,250,514	7,904,349
Accumulated depreciation	(1,359,389)	(1,296,396)
Net real estate investments	6,891,125	6,607,953
Real estate investments and other assets held-for-sale	57,046	30,937
Cash and cash equivalents	21,402	33,889
Accounts receivable, net of allowance	21,073	22,283
Straight-line rent receivable, net of allowance	124,058	120,303
Receivables on construction contracts, including retentions	30,205	39,754
Deferred financing costs, net of accumulated amortization	40,837	40,083
Deferred leasing and other costs, net of accumulated amortization	521,673	497,827
Escrow deposits and other assets	176,483	167,072
Total Assets	7,883,902	7,560,101
LIABILITIES AND EQUITY
Secured debt	1,241,527	1,167,953
Unsecured debt	3,067,250	2,993,217
Unsecured line of credit	88,000	285,000
Long-term debt, total	4,396,777	4,446,170
Liabilities related to real estate investments held-for-sale	749	807
Construction payables and amounts due subcontractors, including retentions	87,730	84,679
Accrued real estate taxes	86,528	74,565
Accrued interest	58,426	59,215
Other accrued expenses	45,026	104,886
Other liabilities	123,649	121,097
Tenant security deposits and prepaid rents	42,755	42,731
Total Liabilities	4,841,640	4,934,150
Equity
Common equity	2,560,701	1,967,091
Preferred equity	447,683	625,638
General Partners' equity	3,008,384	2,592,729
Limited Partners' common equity	20,782	21,383
Accumulated other comprehensive income	3,950	2,691
Total partners' equity	3,033,116	2,616,803
Noncontrolling interests	9,146	9,148
Total Equity	3,042,262	2,625,951
Total Liabilities and Equity	$ 7,883,902	$ 7,560,101