Consolidated Balance Sheets (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Parent Company [Member]
Real estate investments at cost:
Land	$ 1,167,152	$ 1,093,700
Buildings and improvements	2,462,234	2,284,522
Properties in development	521,945	610,932
Gross real estate investments at cost	4,151,331	3,989,154
Less: accumulated depreciation	769,829	700,878
Net real estate investments at cost	3,381,502	3,288,276
Investments in real estate partnerships	425,460	428,592
Net real estate investments	3,806,962	3,716,868
Cash and cash equivalents	21,195	22,460
Accounts receivable, net of allowance for doubtful accounts of $3,862 and $4,819 at September 30, 2011 and December 31, 2010, respectively	29,243	36,600
Straight-line rent receivable, net of allowance of $2,087 and $1,396 at September 30, 2011 and December 31, 2010, respectively	48,327	45,241
Notes receivable	35,931	35,931
Deferred costs, less accumulated amortization of $68,656 and $69,158 at September 30, 2011 and December 31, 2010, respectively	70,006	63,165
Acquired lease intangible assets, less accumulated amortization of $14,562 and $13,996 at September 30, 2011 and December 31, 2010, respectively	26,855	18,219
Trading securities held in trust, at fair value	20,683	20,891
Other assets	36,419	35,164
Total assets	4,095,621	3,994,539
Liabilities:
Notes payable	1,965,340	2,084,469
Unsecured line of credit	85,000	10,000
Accounts payable and other liabilities	114,873	138,196
Acquired lease intangible liabilities, less accumulated accretion of $4,399 and $11,010 at September 30, 2011 and December 31, 2010, respectively	13,694	6,682
Tenants' security and escrow deposits	19,240	10,790
Total liabilities	2,198,147	2,250,137
Commitments and contingencies
Stockholders’ equity/Partners' capital:
Preferred stock, $.01 par value per share, 30,000,000 shares authorized; 11,000,000 Series 3-5 shares issued and outstanding at September 30, 2011 and December 31, 2010 with liquidation preferences of $25 per share	275,000	275,000
Common stock $.01 par value per share, 150,000,000 shares authorized; 89,913,234 and 81,886,872 shares issued at September 30, 2011 and December 31, 2010, respectively	899	819
Treasury stock at cost, 334,188 and 347,482 shares held at September 30, 2011 and December 31, 2010, respectively	(15,028)	(16,175)
Additional paid in capital	2,278,753	2,039,612
Accumulated other comprehensive loss	(73,800)	(80,885)
Distributions in excess of net income	(629,626)	(533,194)
Total stockholders' equity	1,836,198	1,685,177
Noncontrolling interests:
Series D preferred units, aggregate redemption value of $50,000 at September 30, 2011 and December 31, 2010	49,158	49,158
Exchangeable operating partnership units, aggregate redemption value of $6,259 and $7,483 at September 30, 2011 and December 31, 2010, respectively	(917)	(762)
Limited partners' interests in consolidated partnerships	13,035	10,829
Total noncontrolling interests	61,276	59,225
Total equity/capital	1,897,474	1,744,402
Total liabilities and equity/capital	4,095,621	3,994,539
Partnership Interest [Member]
Real estate investments at cost:
Land	1,167,152	1,093,700
Buildings and improvements	2,462,234	2,284,522
Properties in development	521,945	610,932
Gross real estate investments at cost	4,151,331	3,989,154
Less: accumulated depreciation	769,829	700,878
Net real estate investments at cost	3,381,502	3,288,276
Investments in real estate partnerships	425,460	428,592
Net real estate investments	3,806,962	3,716,868
Cash and cash equivalents	21,195	22,460
Accounts receivable, net of allowance for doubtful accounts of $3,862 and $4,819 at September 30, 2011 and December 31, 2010, respectively	29,243	36,600
Straight-line rent receivable, net of allowance of $2,087 and $1,396 at September 30, 2011 and December 31, 2010, respectively	48,327	45,241
Notes receivable	35,931	35,931
Deferred costs, less accumulated amortization of $68,656 and $69,158 at September 30, 2011 and December 31, 2010, respectively	70,006	63,165
Acquired lease intangible assets, less accumulated amortization of $14,562 and $13,996 at September 30, 2011 and December 31, 2010, respectively	26,855	18,219
Trading securities held in trust, at fair value	20,683	20,891
Other assets	36,419	35,164
Total assets	4,095,621	3,994,539
Liabilities:
Notes payable	1,965,340	2,084,469
Unsecured line of credit	85,000	10,000
Accounts payable and other liabilities	114,873	138,196
Acquired lease intangible liabilities, less accumulated accretion of $4,399 and $11,010 at September 30, 2011 and December 31, 2010, respectively	13,694	6,682
Tenants' security and escrow deposits	19,240	10,790
Total liabilities	2,198,147	2,250,137
Commitments and contingencies
Stockholders’ equity/Partners' capital:
Preferred stock, $.01 par value per share, 30,000,000 shares authorized; 11,000,000 Series 3-5 shares issued and outstanding at September 30, 2011 and December 31, 2010 with liquidation preferences of $25 per share	49,158	49,158
Preferred units of general partner, $.01 par value per unit, 11,000,000 units issued and outstanding at September 30, 2011 and December 31, 2010, liquidation preference of $25 per unit	275,000	275,000
General partner; 89,913,234 and 81,886,872 units outstanding at September 30, 2011 and December 31, 2010, respectively	1,634,998	1,491,062
Limited partners; 177,164 units outstanding at September 30, 2011 and December 31, 2010	(917)	(762)
Accumulated other comprehensive loss	(73,800)	(80,885)
Total partners' capital	1,884,439	1,733,573
Noncontrolling interests:
Limited partners' interests in consolidated partnerships	13,035	10,829
Total noncontrolling interests	13,035	10,829
Total equity/capital	1,897,474	1,744,402
Total liabilities and equity/capital	$ 4,095,621	$ 3,994,539