Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Real estate investments at cost (notes 2 and 3):
Properties in development	$ 192,067	$ 224,077
Investments in real estate partnerships (note 4)	442,927	386,882
Restricted cash	6,500	6,000
Accounts receivable, net of allowance for doubtful accounts of $3,915 and $3,442 at December 31, 2012 and 2011, respectively	26,601	37,733
Acquired lease intangible assets, less accumulated amortization of $19,148 and $15,588 at December 31, 2012 and 2011, respectively (note 6)	42,459	27,054
Liabilities:
Acquired lease intangible liabilities, less accumulated accretion of $6,636 and $4,750 at December 31, 2012 and 2011, respectively (note 6)	20,325	12,662
Parent Company [Member]
Real estate investments at cost (notes 2 and 3):
Land	1,215,659	1,273,606
Buildings and improvements	2,502,186	2,604,229
Properties in development	192,067	224,077
Gross real estate investments at cost	3,909,912	4,101,912
Less: accumulated depreciation	782,749	791,619
Total Cost Net of Accumulated Depreciation	3,127,163	3,310,293
Investments in real estate partnerships (note 4)	442,927	386,882
Net real estate investments	3,570,090	3,697,175
Cash and cash equivalents	22,349	11,402
Restricted cash	6,472	6,050
Accounts receivable, net of allowance for doubtful accounts of $3,915 and $3,442 at December 31, 2012 and 2011, respectively	26,601	37,733
Straight-line rent receivable, net of reserve of $870 and $2,075 at December 31, 2012 and 2011, respectively	49,990	48,132
Notes receivable (note 5)	23,751	35,784
Deferred costs, less accumulated amortization of $69,224 and $71,265 at December 31, 2012 and 2011, respectively	69,506	70,204
Acquired lease intangible assets, less accumulated amortization of $19,148 and $15,588 at December 31, 2012 and 2011, respectively (note 6)	42,459	27,054
Trading securities held in trust, at fair value (note 13)	23,429	21,713
Other assets (note 9)	18,811	31,824
Total assets	3,853,458	3,987,071
Liabilities:
Notes payable (note 8)	1,771,891	1,942,440
Unsecured Debt	170,000	40,000
Accounts payable and other liabilities (note 9 and 13)	127,185	101,899
Acquired lease intangible liabilities, less accumulated accretion of $6,636 and $4,750 at December 31, 2012 and 2011, respectively (note 6)	20,325	12,662
Tenants’ security and escrow deposits and prepaid rent	18,146	20,416
Total liabilities	2,107,547	2,117,417
Stockholders’ equity (notes 11 and 12):
Preferred stock, $0.01 par value per share, 30,000,000 shares authorized; 13,000,000 and 11,000,000 Series 3-7 shares issued and outstanding at December 31, 2012 and 2011, respectively, with liquidation preferences of $25 per share	325,000	275,000
Common stock $0.01 par value per share,150,000,000 shares authorized; 90,394,486 and 89,921,858 shares issued at December 31, 2012 and 2011, respectively	904	899
Treasury stock at cost, 335,347 and 338,714 shares held at December 31, 2012 and 2011, respectively	(14,924)	(15,197)
Additional paid in capital	2,312,310	2,281,817
Accumulated other comprehensive loss	(57,715)	(71,429)
Distributions in excess of net income	(834,810)	(662,735)
Total stockholders’ equity	1,730,765	1,808,355
Noncontrolling interests (note 11):
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 $8,348 and $6,665 at December 31, 2012 and 2011, respectively	(1,153)	(963)
Limited partners’ interests in consolidated partnerships	16,299	13,104
Total noncontrolling interests	15,146	61,299
Total equity	1,745,911	1,869,654
Total liabilities and equity	3,853,458	3,987,071
Partnership Interest [Member]
Real estate investments at cost (notes 2 and 3):
Land	1,215,659	1,273,606
Buildings and improvements	2,502,186	2,604,229
Properties in development	192,067	224,077
Gross real estate investments at cost	3,909,912	4,101,912
Less: accumulated depreciation	782,749	791,619
Total Cost Net of Accumulated Depreciation	3,127,163	3,310,293
Investments in real estate partnerships (note 4)	442,927	386,882
Net real estate investments	3,570,090	3,697,175
Cash and cash equivalents	22,349	11,402
Restricted cash	6,472	6,050
Accounts receivable, net of allowance for doubtful accounts of $3,915 and $3,442 at December 31, 2012 and 2011, respectively	26,601	37,733
Straight-line rent receivable, net of reserve of $870 and $2,075 at December 31, 2012 and 2011, respectively	49,990	48,132
Notes receivable (note 5)	23,751	35,784
Deferred costs, less accumulated amortization of $69,224 and $71,265 at December 31, 2012 and 2011, respectively	69,506	70,204
Acquired lease intangible assets, less accumulated amortization of $19,148 and $15,588 at December 31, 2012 and 2011, respectively (note 6)	42,459	27,054
Trading securities held in trust, at fair value (note 13)	23,429	21,713
Other assets (note 9)	18,811	31,824
Total assets	3,853,458	3,987,071
Liabilities:
Notes payable (note 8)	1,771,891	1,942,440
Unsecured Debt	170,000	40,000
Accounts payable and other liabilities (note 9 and 13)	127,185	101,899
Acquired lease intangible liabilities, less accumulated accretion of $6,636 and $4,750 at December 31, 2012 and 2011, respectively (note 6)	20,325	12,662
Tenants’ security and escrow deposits and prepaid rent	18,146	20,416
Total liabilities	2,107,547	2,117,417
Stockholders’ equity (notes 11 and 12):
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, $0.01 par value per unit, 13,000,000 and 11,000,000 units issued and outstanding at December 31, 2012 and 2011, respectively, liquidation preference of $25 per unit	325,000	275,000
General partner; 90,394,486 and 89,921,858 units outstanding at December 31, 2012 and 2011, respectively	1,463,480	1,604,784
Limited partners; 177,164 units outstanding at December 31, 2012 and 2011	(1,153)	(963)
Accumulated other comprehensive loss	(57,715)	(71,429)
Total partners' capital	1,729,612	1,856,550
Noncontrolling interests (note 11):
Limited partners’ interests in consolidated partnerships	16,299	13,104
Total noncontrolling interests	16,299	13,104
Total equity	1,745,911	1,869,654
Total liabilities and equity	$ 3,853,458	$ 3,987,071