Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
ASSETS
Land and improvements	$ 1,457,690	$ 1,438,007
Buildings and tenant improvements	5,605,272	5,531,726
Construction in progress	277,398	256,895
Investments in and advances to unconsolidated companies	336,060	342,947
Undeveloped land	570,718	590,052
Real estate investment property, at cost, total	8,247,138	8,159,627
Accumulated depreciation	(1,419,088)	(1,368,406)
Net real estate investments	6,828,050	6,791,221
Real estate investments and other assets held-for-sale	34,826	57,466
Cash and cash equivalents	19,474	19,275
Accounts receivable, net of allowance	34,763	26,173
Straight-line rent receivable, net of allowance	126,286	118,251
Receivables on construction contracts, including retentions	27,833	19,209
Deferred financing costs, net of accumulated amortization	33,764	36,250
Deferred leasing and other costs, net of accumulated amortization	457,508	466,979
Escrow deposits and other assets	204,859	217,790
Total Assets	7,767,363	7,752,614
LIABILITIES AND EQUITY
Secured debt	1,077,468	1,100,124
Unsecured debt	3,065,742	3,066,252
Unsecured line of credit	180,000	88,000
Long-term debt, total	4,323,210	4,254,376
Liabilities related to real estate investments held-for-sale	179	2,075
Construction payables and amounts due subcontractors, including retentions	72,695	69,380
Accrued real estate taxes	77,169	74,696
Accrued interest	36,468	52,824
Other accrued expenses	52,118	67,495
Other liabilities	138,598	142,589
Tenant security deposits and prepaid rents	50,264	44,550
Total Liabilities	4,750,701	4,707,985
Equity
Preferred shares	428,926	447,683
Common shares	3,285	3,264
Additional paid-in capital	4,649,914	4,620,964
Accumulated other comprehensive income	3,832	4,119
Distributions in excess of net income	(2,100,245)	(2,062,787)
Total shareholders' equity	2,985,712	3,013,243
Noncontrolling interests	30,950	31,386
Total Equity	3,016,662	3,044,629
Total Liabilities and Equity	7,767,363	7,752,614
Subsidiary of Common Parent [Member]
ASSETS
Land and improvements	1,457,690	1,438,007
Buildings and tenant improvements	5,605,272	5,531,726
Construction in progress	277,398	256,895
Investments in and advances to unconsolidated companies	336,060	342,947
Undeveloped land	570,718	590,052
Real estate investment property, at cost, total	8,247,138	8,159,627
Accumulated depreciation	(1,419,088)	(1,368,406)
Net real estate investments	6,828,050	6,791,221
Real estate investments and other assets held-for-sale	34,826	57,466
Cash and cash equivalents	19,474	19,275
Accounts receivable, net of allowance	34,763	26,173
Straight-line rent receivable, net of allowance	126,286	118,251
Receivables on construction contracts, including retentions	27,833	19,209
Deferred financing costs, net of accumulated amortization	33,764	36,250
Deferred leasing and other costs, net of accumulated amortization	457,508	466,979
Escrow deposits and other assets	204,859	217,790
Total Assets	7,767,363	7,752,614
LIABILITIES AND EQUITY
Secured debt	1,077,468	1,100,124
Unsecured debt	3,065,742	3,066,252
Unsecured line of credit	180,000	88,000
Long-term debt, total	4,323,210	4,254,376
Liabilities related to real estate investments held-for-sale	179	2,075
Construction payables and amounts due subcontractors, including retentions	72,695	69,380
Accrued real estate taxes	77,169	74,696
Accrued interest	36,468	52,824
Other accrued expenses	52,362	67,739
Other liabilities	138,598	142,589
Tenant security deposits and prepaid rents	50,264	44,550
Total Liabilities	4,750,945	4,708,229
Equity
Common equity	2,556,883	2,565,370
Preferred equity	428,926	447,683
General Partners' equity	2,985,809	3,013,053
Limited Partners' common equity	19,662	20,158
Accumulated other comprehensive income	3,832	4,119
Total partners' equity	3,009,303	3,037,330
Noncontrolling interests	7,115	7,055
Total Equity	3,016,418	3,044,385
Total Liabilities and Equity	$ 7,767,363	$ 7,752,614