Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012 Parent Company [Member]	Jun. 30, 2011 Parent Company [Member]	Jun. 30, 2012 Parent Company [Member]	Jun. 30, 2011 Parent Company [Member]	Jun. 30, 2012 Partnership Interest [Member]	Jun. 30, 2011 Partnership Interest [Member]	Jun. 30, 2012 Partnership Interest [Member]	Jun. 30, 2011 Partnership Interest [Member]
Revenues
Minimum rent	$ 92,725	$ 87,000	$ 184,602	$ 173,728	$ 92,725	$ 87,000	$ 184,602	$ 173,728
Percentage rent	398	151	1,558	1,058	398	151	1,558	1,058
Recoveries from tenants and other income	30,175	25,299	56,742	53,493	30,175	25,299	56,742	53,493
Management, transaction, and other fees	6,469	12,193	13,618	20,053	6,469	12,193	13,618	20,053
Total revenues	129,767	124,643	256,520	248,332	129,767	124,643	256,520	248,332
Operating Expenses
Depreciation and amortization	33,045	31,219	65,710	65,550	33,045	31,219	65,710	65,550
Operating and maintenance	17,806	17,232	36,327	36,141	17,806	17,232	36,327	36,141
General and administrative	14,020	15,177	30,142	32,130	14,020	15,177	30,142	32,130
Real estate taxes	14,143	13,712	29,322	27,956	14,143	13,712	29,322	27,956
Other expenses	269	2,255	1,858	1,936	269	2,255	1,858	1,936
Total operating expenses	79,283	79,595	163,359	163,713	79,283	79,595	163,359	163,713
Other expense (income):
Interest expense, net of interest income of $377 and $587, and $913 and $1,188 for the three and six months ended June 30, 2012 and 2011, respectively	28,377	30,563	57,335	61,428	28,377	30,563	57,335	61,428
Loss (gain) on sale of real estate	21	0	(1,814)	0	21	0	(1,814)	0
Provision for impairment	23,508	0	23,508	0	23,508	0	23,508	0
Net investment income (loss) from deferred compensation plan, including unrealized (loss) gains of $(449) and $88, and $725 and $731 for the three and six months ended June 30, 2012 and 2011, respectively	444	(143)	(1,084)	(888)	444	(143)	(1,084)	(888)
Total other expense (income)	52,350	30,420	77,945	60,540	52,350	30,420	77,945	60,540
(Loss) income before equity in income (loss) of investments in real estate partnerships	(1,866)	14,628	15,216	24,079	(1,866)	14,628	15,216	24,079
Equity in income (loss) of investments in real estate partnerships	10,804	2,688	13,770	(37)	10,804	2,688	13,770	(37)
Income from continuing operations	8,938	17,316	28,986	24,042	8,938	17,316	28,986	24,042
Discontinued operations, net:
Operating income	106	1,621	492	3,025	106	1,621	492	3,025
Gain on sale of operating properties, net	2,304	0	8,605	0	2,304	0	8,605	0
Income from discontinued operations	2,410	1,621	9,097	3,025	2,410	1,621	9,097	3,025
Net income	11,348	18,937	38,083	27,067	11,348	18,937	38,083	27,067
Noncontrolling interests:
Preferred units	0	(931)	629	(1,862)
Exchangeable operating partnership units	(23)	(37)	(77)	(50)
Limited partners' interest in consolidated partnerships	(232)	(189)	(424)	(271)	(232)	(189)	(424)	(271)
(Income) loss attributable to noncontrolling interests	(255)	(1,157)	128	(2,183)	(232)	(189)	(424)	(271)
Net income attributable to controlling interests	11,093	17,780	38,211	24,884	11,116	18,748	37,659	26,796
Preferred stock dividends	(5,396)	(4,919)	(19,333)	(9,838)
Preferred unit distributions					(5,396)	(5,850)	(18,704)	(11,700)
Net income attributable to common stockholders	5,697	12,861	18,878	15,046
Net income attributable to common unit holders					$ 5,720	$ 12,898	$ 18,955	$ 15,096
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.03	$ 0.12	$ 0.11	$ 0.13
Continuing operations (in dollars per share)					0.03	0.12	0.11	0.13
Discontinued operations (in dollars per share)	$ 0.03	$ 0.02	$ 0.10	$ 0.04
Discontinued operations (in dollars per share)					0.03	0.02	0.10	0.04
Net income attributable to common stockholders (in dollars per share)	$ 0.06	$ 0.14	$ 0.21	$ 0.17
Net income attributable to common unit holders (in dollars per share)					0.06	0.14	0.21	0.17
Income per common share/unit - diluted:
Continuing operations (in dollars per share)					0.03	0.12	0.11	0.13
Continuing operations (in dollars per share)	$ 0.03	$ 0.12	$ 0.11	$ 0.13
Discontinued operations (in dollars per share)					0.03	0.02	0.10	0.04
Discontinued operations (in dollars per share)	$ 0.03	$ 0.02	$ 0.10	$ 0.04
Net income attributable to common stockholders (in dollars per share)	$ 0.06	$ 0.14	$ 0.21	$ 0.17
Net Income (Loss), Per Outstanding Limited Partnership Unit, Diluted					0.06	0.14	0.21	0.17