Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Liabilities:
Unsecured credit facilities	$ 65,000	$ 40,000
Parent Company [Member]
Real estate investments at cost:
Land	1,212,308	1,273,606
Buildings and improvements	2,398,114	2,604,229
Properties in development	220,753	224,077
Gross real estate investments at cost	3,831,175	4,101,912
Less: accumulated depreciation	768,301	791,619
Total Cost Net of Accumulated Depreciation	3,062,874	3,310,293
Investments in real estate partnerships	450,021	386,882
Net real estate investments	3,512,895	3,697,175
Cash and cash equivalents	21,350	11,402
Restricted cash	6,133	6,050
Accounts receivable, net of allowance for doubtful accounts of $3,759 and $3,442 at September 30, 2012 and and December 31, 2011, respectively	28,220	37,733
Straight-line rent receivable, net of allowance of $870 and $2,075 at September 30, 2012 and December 31, 2011, respectively	48,677	48,132
Notes receivable	23,777	35,784
Deferred costs, less accumulated amortization of $66,477 and $71,265 at September 30, 2012 and December 31, 2011, respectively	68,141	70,204
Acquired lease intangible assets, less accumulated amortization of $17,482 and $15,588 at September 30, 2012 and December 31, 2011, respectively	35,581	27,054
Trading securities held in trust, at fair value	23,208	21,713
Other assets	29,992	31,824
Total assets	3,797,974	3,987,071
Liabilities:
Notes payable	1,756,412	1,942,440
Unsecured credit facilities	65,000	40,000
Accounts payable and other liabilities	129,483	101,862
Derivative instruments, at fair value	86	37
Acquired lease intangible liabilities, less accumulated accretion of $5,947 and $4,750 at September 30, 2012 and December 31, 2011, respectively	18,506	12,662
Tenants' security and escrow deposits and prepaid rent	14,053	20,416
Total liabilities	1,983,540	2,117,417
Commitments and contingencies (note 10)
Stockholders’ equity/Partners' capital:
Preferred stock, $.01 par value per share, 30,000,000 shares authorized; 13,000,000 and 11,000,000 Series 3-7 shares issued and outstanding at September 30, 2012 and December 31, 2011, respectively, with liquidation preferences of $25 per share	325,000	275,000
Common stock $.01 par value per share, 150,000,000 shares authorized; 90,387,798 and 89,921,858 shares issued at September 30, 2012 and December 31, 2011, respectively	904	899
Treasury stock at cost, 331,754 and 338,714 shares held at September 30, 2012 and December 31, 2011, respectively	(14,756)	(15,197)
Additional paid in capital	2,308,681	2,281,817
Accumulated other comprehensive loss	(64,378)	(71,429)
Distributions in excess of net income	(756,114)	(662,735)
Total stockholders' equity	1,799,337	1,808,355
Noncontrolling interests:
Series D preferred units, aggregate redemption value of $50,000 at December 31, 2011	0	49,158
Exchangeable operating partnership units, aggregate redemption value of $8,633 and $6,665 at September 30, 2012 and December 31, 2011, respectively	(1,079)	(963)
Limited partners' interests in consolidated partnerships	16,176	13,104
Total noncontrolling interests	15,097	61,299
Total equity/capital	1,814,434	1,869,654
Total liabilities and equity/capital	3,797,974	3,987,071
Partnership Interest [Member]
Real estate investments at cost:
Land	1,212,308	1,273,606
Buildings and improvements	2,398,114	2,604,229
Properties in development	220,753	224,077
Gross real estate investments at cost	3,831,175	4,101,912
Less: accumulated depreciation	768,301	791,619
Total Cost Net of Accumulated Depreciation	3,062,874	3,310,293
Investments in real estate partnerships	450,021	386,882
Net real estate investments	3,512,895	3,697,175
Cash and cash equivalents	21,350	11,402
Restricted cash	6,133	6,050
Accounts receivable, net of allowance for doubtful accounts of $3,759 and $3,442 at September 30, 2012 and and December 31, 2011, respectively	28,220	37,733
Straight-line rent receivable, net of allowance of $870 and $2,075 at September 30, 2012 and December 31, 2011, respectively	48,677	48,132
Notes receivable	23,777	35,784
Deferred costs, less accumulated amortization of $66,477 and $71,265 at September 30, 2012 and December 31, 2011, respectively	68,141	70,204
Acquired lease intangible assets, less accumulated amortization of $17,482 and $15,588 at September 30, 2012 and December 31, 2011, respectively	35,581	27,054
Trading securities held in trust, at fair value	23,208	21,713
Other assets	29,992	31,824
Total assets	3,797,974	3,987,071
Liabilities:
Notes payable	1,756,412	1,942,440
Unsecured credit facilities	65,000	40,000
Accounts payable and other liabilities	129,483	101,862
Derivative instruments, at fair value	86	37
Acquired lease intangible liabilities, less accumulated accretion of $5,947 and $4,750 at September 30, 2012 and December 31, 2011, respectively	18,506	12,662
Tenants' security and escrow deposits and prepaid rent	14,053	20,416
Total liabilities	1,983,540	2,117,417
Stockholders’ equity/Partners' capital:
Series D preferred units, par value $100: 500,000 units issued and outstanding at December 31, 2011	0	49,158
Preferred units of general partner, $.01 par value per unit, 13,000,000 and 11,000,000 units issued and outstanding at September 30, 2012 and December 31, 2011, respectively, liquidation preference of $25 per unit	325,000	275,000
General partner; 90,387,798 and 89,921,858 units outstanding at September 30, 2012 and December 31, 2011, respectively	1,538,715	1,604,784
Limited partners; 177,164 units outstanding at September 30, 2012 and December 31, 2011	(1,079)	(963)
Accumulated other comprehensive loss	(64,378)	(71,429)
Total partners' capital	1,798,258	1,856,550
Noncontrolling interests:
Limited partners' interests in consolidated partnerships	16,176	13,104
Total noncontrolling interests	16,176	13,104
Total equity/capital	1,814,434	1,869,654
Total liabilities and equity/capital	$ 3,797,974	$ 3,987,071