Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Parent Company [Member]
Revenues:
Minimum rent	$ 94,536	$ 86,146
Percentage rent	1,384	1,544
Recoveries from tenants and other income	31,041	25,927
Management, transaction, and other fees	6,319	6,761
Total revenues	133,280	120,378
Operating expenses:
Depreciation and amortization	37,905	31,118
Operating and maintenance	20,505	17,141
General and administrative	14,198	17,975
Real estate taxes	14,799	13,231
Other expenses	2,173	1,517
Total operating expenses	89,580	80,982
Other expense (income):
Interest expense, net of interest income of $216 and $459 for the three months ended March 31, 2014 and 2013, respectively	27,134	27,832
Provision for impairment	225	0
Net investment income from deferred compensation plan, including unrealized loss (gains) of $107 and ($831) for the three months ended March 31, 2014 and 2013, respectively	(192)	(1,071)
Total other expense	27,167	26,761
Income before equity in income of investments in real estate partnerships	16,533	12,635
Equity in income of investments in real estate partnerships	7,808	5,876
Income from continuing operations	24,341	18,511
Discontinued operations, net:
Operating income	0	2,623
Income from discontinued operations	0	2,623
Income before gain on sale of real estate	24,341	21,134
Gain on sale of real estate	(715)	0
Net income	25,056	21,134
Noncontrolling interests:
Exchangeable operating partnership units	(42)	(39)
Limited partners’ interests in consolidated partnerships	(359)	(275)
Income attributable to noncontrolling interests	(401)	(314)
Net income attributable to the Company	24,655	20,820
Preferred stock dividends	(5,266)	(5,266)
Net income attributable to common stockholders	19,389	15,554
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.21	$ 0.14
Discontinued operations (in dollars per share)	$ 0.00	$ 0.03
Net income attributable to common stockholders (in dollars per share)	$ 0.21	$ 0.17
Income per common share/unit - diluted:
Continuing operations (in dollars per share)	$ 0.21	$ 0.14
Discontinued operations (in dollars per share)	$ 0.00	$ 0.03
Net income attributable to common stockholders (in dollars per share)	$ 0.21	$ 0.17
Partnership Interest [Member]
Revenues:
Minimum rent	94,536	86,146
Percentage rent	1,384	1,544
Recoveries from tenants and other income	31,041	25,927
Management, transaction, and other fees	6,319	6,761
Total revenues	133,280	120,378
Operating expenses:
Depreciation and amortization	37,905	31,118
Operating and maintenance	20,505	17,141
General and administrative	14,198	17,975
Real estate taxes	14,799	13,231
Other expenses	2,173	1,517
Total operating expenses	89,580	80,982
Other expense (income):
Interest expense, net of interest income of $216 and $459 for the three months ended March 31, 2014 and 2013, respectively	27,134	27,832
Provision for impairment	225	0
Net investment income from deferred compensation plan, including unrealized loss (gains) of $107 and ($831) for the three months ended March 31, 2014 and 2013, respectively	(192)	(1,071)
Total other expense	27,167	26,761
Income before equity in income of investments in real estate partnerships	16,533	12,635
Equity in income of investments in real estate partnerships	7,808	5,876
Income from continuing operations	24,341	18,511
Discontinued operations, net:
Operating income	0	2,623
Income from discontinued operations	0	2,623
Income before gain on sale of real estate	24,341	21,134
Gain on sale of real estate	(715)	0
Net income	25,056	21,134
Noncontrolling interests:
Limited partners’ interests in consolidated partnerships	(359)	(275)
Income attributable to noncontrolling interests	(359)	(275)
Net income attributable to the Company	24,697	20,859
Preferred unit distributions	(5,266)	(5,266)
Net income attributable to common unit holders	$ 19,431	$ 15,593
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.21	$ 0.14
Discontinued operations (in dollars per share)	$ 0.00	$ 0.03
Net income attributable to common unit holders (in dollars per share)	$ 0.21	$ 0.17
Income per common share/unit - diluted:
Continuing operations (in dollars per share)	$ 0.21	$ 0.14
Discontinued operations (in dollars per share)	$ 0.00	$ 0.03
Net income attributable to common unit holders (in dollars per share)	$ 0.21	$ 0.17