Consolidated Statements of Operations (USD $)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012 Parent Company [Member]	Sep. 30, 2011 Parent Company [Member]	Sep. 30, 2012 Parent Company [Member]	Sep. 30, 2011 Parent Company [Member]	Sep. 30, 2012 Partnership Interest [Member]	Sep. 30, 2011 Partnership Interest [Member]	Sep. 30, 2012 Partnership Interest [Member]	Sep. 30, 2011 Partnership Interest [Member]
Revenues
Minimum rent	$ 88,003,000	$ 87,974,000	$ 272,590,000	$ 261,702,000	$ 88,003,000	$ 87,974,000	$ 272,590,000	$ 261,702,000
Percentage rent	378,000	430,000	1,935,000	1,487,000	378,000	430,000	1,935,000	1,487,000
Recoveries from tenants and other income	25,191,000	27,676,000	81,933,000	81,170,000	25,191,000	27,676,000	81,933,000	81,170,000
Management, transaction, and other fees	6,441,000	6,940,000	20,060,000	26,993,000	6,441,000	6,940,000	20,060,000	26,993,000
Total revenues	120,013,000	123,020,000	376,518,000	371,352,000	120,013,000	123,020,000	376,518,000	371,352,000
Operating Expenses
Depreciation and amortization	30,155,000	32,497,000	95,866,000	98,047,000	30,155,000	32,497,000	95,866,000	98,047,000
Operating and maintenance	16,389,000	17,693,000	52,702,000	53,833,000	16,389,000	17,693,000	52,702,000	53,833,000
General and administrative	15,641,000	11,671,000	45,783,000	43,801,000	15,641,000	11,671,000	45,783,000	43,801,000
Real estate taxes	13,306,000	13,181,000	42,628,000	41,137,000	13,306,000	13,181,000	42,628,000	41,137,000
Other expenses	1,660,000	2,194,000	3,516,000	4,130,000	1,660,000	2,194,000	3,516,000	4,130,000
Total operating expenses	77,151,000	77,236,000	240,495,000	240,948,000	77,151,000	77,236,000	240,495,000	240,948,000
Other expense (income):
Interest expense, net of interest income of $379 and $613, and $1,291 and $1,802 for the three and nine months ended September 30, 2012 and 2011, respectively	27,462,000	30,867,000	84,796,000	92,297,000	27,462,000	30,867,000	84,796,000	92,297,000
Gain on sale of real estate	(228,000)	0	(2,041,000)	0	(228,000)	0	(2,041,000)	0
Provision for impairment	1,147,000	6,362,000	24,655,000	6,362,000	1,147,000	6,362,000	24,655,000	6,362,000
Early extinguishment of debt	852,000	0	852,000	0	852,000	0	852,000	0
Net investment income (loss) from deferred compensation plan, including unrealized (loss) gains of $(618) and $2,313, and $(1,343) and $1,582 for the three and nine months ended September 30, 2012 and 2011, respectively	(752,000)	2,283,000	(1,836,000)	1,395,000	(752,000)	2,283,000	(1,836,000)	1,395,000
Total other expense (income)	28,481,000	39,512,000	106,426,000	100,054,000	28,481,000	39,512,000	106,426,000	100,054,000
Income before equity in income of investments in real estate partnerships	14,381,000	6,272,000	29,597,000	30,350,000	14,381,000	6,272,000	29,597,000	30,350,000
Equity in income of investments in real estate partnerships	5,403,000	4,825,000	19,173,000	4,788,000	5,403,000	4,825,000	19,173,000	4,788,000
Income from continuing operations	19,784,000	11,097,000	48,770,000	35,138,000	19,784,000	11,097,000	48,770,000	35,138,000
Discontinued operations, net:
Operating income	36,000	1,123,000	528,000	4,149,000	36,000	1,123,000	528,000	4,149,000
Gain on sale of operating properties, net	0	2,321,000	8,605,000	2,321,000	0	2,321,000	8,605,000	2,321,000
Income from discontinued operations	36,000	3,444,000	9,133,000	6,470,000	36,000	3,444,000	9,133,000	6,470,000
Net income	19,820,000	14,541,000	57,903,000	41,608,000	19,820,000	14,541,000	57,903,000	41,608,000
Noncontrolling interests:
Preferred units	0	(931,000)	629,000	(2,794,000)
Exchangeable operating partnership units	(39,000)	(27,000)	(116,000)	(77,000)
Limited partners' interest in consolidated partnerships	(212,000)	(154,000)	(636,000)	(425,000)	(212,000)	(154,000)	(636,000)	(425,000)
Income attributable to noncontrolling interests	(251,000)	(1,112,000)	(123,000)	(3,296,000)	(212,000)	(154,000)	(636,000)	(425,000)
Net income attributable to controlling interests	19,569,000	13,429,000	57,780,000	38,312,000	19,608,000	14,387,000	57,267,000	41,183,000
Preferred stock dividends	(7,932,000)	(4,919,000)	(27,265,000)	(14,756,000)
Preferred unit distributions					(7,932,000)	(5,850,000)	(26,636,000)	(17,550,000)
Net income attributable to common stockholders	11,637,000	8,510,000	30,515,000	23,556,000
Net income attributable to common unit holders					$ 11,676,000	$ 8,537,000	$ 30,631,000	$ 23,633,000
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.13	$ 0.05	$ 0.24	$ 0.19
Continuing operations (in dollars per share)					0.13	0.05	0.24	0.19
Discontinued operations (in dollars per share)	$ 0.00	$ 0.04	$ 0.10	$ 0.07
Discontinued operations (in dollars per share)					0.00	0.04	0.10	0.07
Net income attributable to common stockholders (in dollars per share)	$ 0.13	$ 0.09	$ 0.34	$ 0.26
Net income attributable to common unit holders (in dollars per share)					0.13	0.09	0.34	0.26
Income per common share/unit - diluted:
Continuing operations (in dollars per share)					0.13	0.05	0.24	0.19
Continuing operations (in dollars per share)	$ 0.13	$ 0.05	$ 0.24	$ 0.19
Discontinued operations (in dollars per share)					0.00	0.04	0.10	0.07
Discontinued operations (in dollars per share)	$ 0.00	$ 0.04	$ 0.10	$ 0.07
Net income attributable to common stockholders (in dollars per share)	$ 0.13	$ 0.09	$ 0.34	$ 0.26
Net Income (Loss), Per Outstanding Limited Partnership Unit, Diluted					0.13	0.09	0.34	0.26