Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Real estate investments at cost:
Land	$ 1,273,606
Properties in development	224,077	610,932
Gross real estate investments at cost	4,101,912
Less: accumulated depreciation	791,619
Total Cost Net of Accumulated Depreciation	3,310,293
Investments in real estate partnerships	386,882	428,592
Restricted Cash	6,000	5,400
Accounts receivable, net of allowance for doubtful accounts of $3,442 and $4,819 at December 31, 2011 and 2010, respectively	37,733	36,600
Liabilities:
Acquired lease intangible liabilities, less accumulated accretion of $4,750 and $11,010 at December 31, 2011 and 2010, respectively	12,700	6,700
Parent Company [Member]
Real estate investments at cost:
Land	1,273,606	1,093,700
Buildings and improvements	2,604,229	2,284,522
Properties in development	224,077	610,932
Gross real estate investments at cost	4,101,912	3,989,154
Less: accumulated depreciation	791,619	700,878
Total Cost Net of Accumulated Depreciation	3,310,293	3,288,276
Investments in real estate partnerships	386,882	428,592
Net real estate investments	3,697,175	3,716,868
Cash and cash equivalents (including $6,050 and $5,399 million of restricted cash at December 31, 2011 and 2010, respectively)	11,402	17,061
Restricted Cash	6,050	5,399
Accounts receivable, net of allowance for doubtful accounts of $3,442 and $4,819 at December 31, 2011 and 2010, respectively	37,733	36,600
Straight-line rent receivable, net of allowance of $2,075 and $1,396 at December 31, 2011 and 2010, respectively	48,132	45,241
Notes receivable	35,784	35,931
Deferred costs, less accumulated amortization of $71,265 and $69,158 at December 31, 2011 and 2010, respectively	70,204	63,165
Acquired lease intangible assets, less accumulated amortization of $15,588 and $13,996 at December 31, 2011 and 2010, respectively	27,054	18,219
Trading securities held in trust, at fair value	21,713	20,891
Other assets	31,824	35,164
Total assets	3,987,071	3,994,539
Liabilities:
Notes payable	1,942,440	2,084,469
Unsecured line of credit	40,000	10,000
Accounts payable and other liabilities	101,862	138,196
Derivative Liabilities	37	0
Acquired lease intangible liabilities, less accumulated accretion of $4,750 and $11,010 at December 31, 2011 and 2010, respectively	12,662	6,682
Tenants' security and escrow deposits	20,416	10,790
Total liabilities	2,117,417	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 December 31, 2011 and 2010 with liquidation preferences of $25 per share	275,000	275,000
Common stock $.01 par value per share, 150,000,000 shares authorized; 89,921,858 and 81,886,872 shares issued at December 31, 2011 and 2010, respectively	899	819
Treasury stock at cost, 338,714 and 347,482 shares held at December 31, 2011 and 2010, respectively	(15,197)	(16,175)
Additional paid in capital	2,281,817	2,039,612
Accumulated other comprehensive loss	(71,429)	(80,885)
Distributions in excess of net income	(662,735)	(533,194)
Total stockholders' equity	1,808,355	1,685,177
Noncontrolling interests:
Series D preferred units, aggregate redemption value of $50,000 at December 31, 2011 and 2010	49,158	49,158
Exchangeable operating partnership units, aggregate redemption value of $6,665 and $7,483 at December 31, 2011 and 2010, respectively	(963)	(762)
Limited partners' interests in consolidated partnerships	13,104	10,829
Total noncontrolling interests	61,299	59,225
Total equity/capital	1,869,654	1,744,402
Total liabilities and equity/capital	3,987,071	3,994,539
Partnership Interest [Member]
Real estate investments at cost:
Land	1,273,606	1,093,700
Buildings and improvements	2,604,229	2,284,522
Properties in development	224,077	610,932
Gross real estate investments at cost	4,101,912	3,989,154
Less: accumulated depreciation	791,619	700,878
Total Cost Net of Accumulated Depreciation	3,310,293	3,288,276
Investments in real estate partnerships	386,882	428,592
Net real estate investments	3,697,175	3,716,868
Cash and cash equivalents (including $6,050 and $5,399 million of restricted cash at December 31, 2011 and 2010, respectively)	11,402	17,061
Restricted Cash	6,050	5,399
Accounts receivable, net of allowance for doubtful accounts of $3,442 and $4,819 at December 31, 2011 and 2010, respectively	37,733	36,600
Straight-line rent receivable, net of allowance of $2,075 and $1,396 at December 31, 2011 and 2010, respectively	48,132	45,241
Notes receivable	35,784	35,931
Deferred costs, less accumulated amortization of $71,265 and $69,158 at December 31, 2011 and 2010, respectively	70,204	63,165
Acquired lease intangible assets, less accumulated amortization of $15,588 and $13,996 at December 31, 2011 and 2010, respectively	27,054	18,219
Trading securities held in trust, at fair value	21,713	20,891
Other assets	31,824	35,164
Total assets	3,987,071	3,994,539
Liabilities:
Notes payable	1,942,440	2,084,469
Unsecured line of credit	40,000	10,000
Accounts payable and other liabilities	101,862	138,196
Derivative Liabilities	37	0
Acquired lease intangible liabilities, less accumulated accretion of $4,750 and $11,010 at December 31, 2011 and 2010, respectively	12,662	6,682
Tenants' security and escrow deposits	20,416	10,790
Total liabilities	2,117,417	2,250,137
Stockholders’ equity/Partners' capital:
Series D preferred units, par value $100: 500,000 units issued and outstanding at December 31, 2011 and 2010	49,158	49,158
Preferred units of general partner, $.01 par value per unit, 11,000,000 units issued and outstanding at December 31, 2011 and 2010, liquidation preference of $25 per unit	275,000	275,000
General partner; 89,921,858 and 81,886,872 units outstanding at December 31, 2011 and 2010, respectively	1,604,784	1,491,062
Limited partners; 177,164 units outstanding at December 31, 2011 and 2010	(963)	(762)
Accumulated other comprehensive loss	(71,429)	(80,885)
Total partners' capital	1,856,550	1,733,573
Noncontrolling interests:
Limited partners' interests in consolidated partnerships	13,104	10,829
Total noncontrolling interests	13,104	10,829
Total equity/capital	1,869,654	1,744,402
Total liabilities and equity/capital	$ 3,987,071	$ 3,994,539