Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013 Parent Company [Member]	Dec. 31, 2012 Parent Company [Member]	Dec. 31, 2013 Partnership Interest [Member]	Dec. 31, 2012 Partnership Interest [Member]
Real estate investments at cost (notes 2 and 3):
Land	$ 1,249,779	$ 1,215,659	$ 1,249,779	$ 1,215,659
Buildings and improvements	2,590,302	2,502,186	2,590,302	2,502,186
Properties in development	186,450	192,067	186,450	192,067
Gross real estate investments at cost	4,026,531	3,909,912	4,026,531	3,909,912
Less: accumulated depreciation	844,873	782,749	844,873	782,749
Total Cost Net of Accumulated Depreciation	3,181,658	3,127,163	3,181,658	3,127,163
Investments in real estate partnerships (note 4)	358,849	442,927	358,849	442,927
Net real estate investments	3,540,507	3,570,090	3,540,507	3,570,090
Cash and cash equivalents	80,684	22,349	80,684	22,349
Restricted cash	9,520	6,472	9,520	6,472
Accounts receivable, net of allowance for doubtful accounts of $3,922 and $3,915 at December 31, 2013 and 2012, respectively	26,319	26,601	26,319	26,601
Straight-line rent receivable, net of reserve of $547 and $870 at December 31, 2013 and 2012, respectively	50,612	49,990	50,612	49,990
Notes receivable (note 5)	11,960	23,751	11,960	23,751
Deferred costs, less accumulated amortization of $73,231 and $69,224 at December 31, 2013 and 2012, respectively	69,963	69,506	69,963	69,506
Acquired lease intangible assets, less accumulated amortization of $25,591 and $19,148 at December 31, 2013 and 2012, respectively (note 6)	44,805	42,459	44,805	42,459
Trading securities held in trust, at fair value (note 13)	26,681	23,429	26,681	23,429
Other assets (note 9)	52,465	18,811	52,465	18,811
Total assets	3,913,516	3,853,458	3,913,516	3,853,458
Liabilities:
Notes payable (note 8)	1,779,697	1,771,891	1,779,697	1,771,891
Unsecured Debt	75,000	170,000	75,000	170,000
Accounts payable and other liabilities (note 9 and 13)	147,045	127,185	147,045	127,185
Acquired lease intangible liabilities, less accumulated accretion of $10,102 and $6,636 at December 31, 2013 and 2012, respectively (note 6)	26,729	20,325	26,729	20,325
Tenants’ security and escrow deposits and prepaid rent	23,911	18,146	23,911	18,146
Total liabilities	2,052,382	2,107,547	2,052,382	2,107,547
Commitments and contingencies (notes 15 and 16)	0	0	0	0
Stockholders’ equity (notes 11 and 12):
Preferred stock, $0.01 par value per share, 30,000,000 shares authorized; 13,000,000 Series 6 and 7 shares issued and outstanding at December 31, 2013 and December 31, 2012, with liquidation preferences of $25 per share	325,000	325,000
Preferred Units General Partner			325,000	325,000
General partner; 92,333,161 and 90,394,486 units outstanding at December 31, 2013 and 2012, respectively			1,535,758	1,463,480
Limited partners; 165,796 and 177,164 units outstanding at December 31, 2013 and 2012, respectively			(1,426)	(1,153)
Common stock $0.01 par value per share,150,000,000 shares authorized; 92,333,161 and 90,394,486 shares issued at December 31, 2013 and 2012, respectively	923	904
Treasury stock at cost, 373,042 and 335,347 shares held at December 31, 2013 and 2012, respectively	(16,726)	(14,924)
Additional paid in capital	2,426,477	2,312,310
Accumulated other comprehensive loss	(17,404)	(57,715)	(17,404)	(57,715)
Distributions in excess of net income	(874,916)	(834,810)
Total stockholders’ equity	1,843,354	1,730,765
Total partners' capital			1,841,928	1,729,612
Noncontrolling interests (note 11):
Exchangeable operating partnership units, aggregate redemption value of $7,676 and $8,348 at December 31, 2013 and 2012, respectively	(1,426)	(1,153)
Limited partners’ interests in consolidated partnerships	19,206	16,299	19,206	16,299
Total noncontrolling interests	17,780	15,146	19,206	16,299
Total equity	1,861,134	1,745,911	1,861,134	1,745,911
Total liabilities and equity	$ 3,913,516	$ 3,853,458	$ 3,913,516	$ 3,853,458