Earnings per Share and Unit (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Document Fiscal Year Focus			2014
Document Period End Date			Sep. 30, 2014
Earnings Per Share [Abstract]
Gain on sale of real estate, net of tax	$ 27,558	$ 16,108	$ 29,598	$ 29,235
Income per common unit - diluted
Weighted Average Limited Partnership Units Outstanding, Basic	158,920	167,649	159,229	173,946
Parent Company [Member]
Earnings Per Share [Abstract]
Income from continuing operations	25,882	23,016	80,061	63,170
Gain on sale of real estate, net of tax	27,558	56	29,598	1,773
Less: income (loss) attributable to noncontrolling interests	232	367	1,048	990
Income from continuing operations attributable to the Company	53,208	22,705	108,611	63,953
Preferred stock dividends	(5,266)	(5,266)	(15,797)	(15,797)
Less: dividends paid on unvested restricted stock	149	148	448	445
Net income attributable to common stockholders	47,793	34,850	92,366	81,971
Add: dividends paid on Treasury Method restricted stock	(24)	(15)	50	55
Net income for common stock unit/holders - diluted	47,817	34,865	92,416	82,026
Income from discontinued operations	0	17,592	0	34,325
Less: income from discontinued operations attributable to noncontrolling interests	0	33	0	65
Income from discontinued operations attributable to the Company	0	17,559	0	34,260
Weighted average common units outstanding for basic EPU (in shares)	92,345,000	91,985,000	92,071,000	91,147,000
Incremental units to be issued under unvested restricted stock (in shares)	51,000	33,000	36,000	40,000
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements			0	0
Weighted average common units outstanding for diluted EPU (in shares)	92,396,000	92,018,000	92,107,000	91,187,000
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.52	$ 0.19	$ 1.00	$ 0.52
Discontinued operations (in dollars per share)	$ 0.00	$ 0.19	$ 0.00	$ 0.38
Net income attributable to common stockholders (in dollars per share)	$ 0.52	$ 0.38	$ 1.00	$ 0.90
Income per common share/unit - diluted:
Continuing operations (in dollars per share)	$ 0.52	$ 0.19	$ 1.00	$ 0.52
Discontinued operations (in dollars per share)	$ 0.00	$ 0.19	$ 0.00	$ 0.38
Net income attributable to common stockholders (in dollars per share)	$ 0.52	$ 0.38	$ 1.00	$ 0.90
Partnership Interest [Member]
Earnings Per Share [Abstract]
Income from continuing operations	25,882	23,016	80,061	63,170
Gain on sale of real estate, net of tax	27,558	56	29,598	1,773
Income from continuing operations attributable to the Company	53,298	22,778	108,796	64,136
Less: dividends paid on unvested restricted stock	149	148	448	445
Net income attributable to common stockholders	47,883	34,923	92,551	82,154
Add: dividends paid on Treasury Method restricted stock	(24)	(15)	(50)	(55)
Net income for common stock unit/holders - diluted	47,907	34,938	92,601	82,209
Income from discontinued operations	0	17,592	0	34,325
Less: income from discontinued operations attributable to noncontrolling interests		33		65
Income from discontinued operations attributable to the Company	0	17,559	0	34,260
Less: preferred unit distributions	5,266	5,266	15,797	15,797
Weighted average common units outstanding for basic EPU (in shares)	92,505,000	92,153,000	92,231,000	91,321,000
Incremental units to be issued under unvested restricted stock (in shares)	51,000	33,000	36,000	40,000
Weighted average common units outstanding for diluted EPU (in shares)	92,556,000	92,186,000	92,267,000	91,361,000
Income per common unit - basic
Continuing operations (in dollars per share)	$ 0.52	$ 0.19	$ 1.00	$ 0.52
Discontinued operations (in dollars per share)	$ 0.00	$ 0.19	$ 0.00	$ 0.38
Net income attributable to common unit holders (in dollars per share)	$ 0.52	$ 0.38	$ 1.00	$ 0.90
Income per common unit - diluted
Continuing operations (in dollars per share)	$ 0.52	$ 0.19	$ 1.00	$ 0.52
Discontinued operations (in dollars per share)	$ 0.00	$ 0.19	$ 0.00	$ 0.38
Net income attributable to common unit holders (in dollars per share)	$ 0.52	$ 0.38	$ 1.00	$ 0.90
Continuing Operations [Member] | Parent Company [Member]
Earnings Per Share [Abstract]
Net income attributable to common stockholders	47,793	17,291	92,366	47,711
Net income for common stock unit/holders - diluted	47,817	17,306	92,416	47,766
Continuing Operations [Member] | Partnership Interest [Member]
Earnings Per Share [Abstract]
Less: income (loss) attributable to noncontrolling interests	142	294	863	807
Net income attributable to common stockholders	47,883	17,364	92,551	47,894
Net income for common stock unit/holders - diluted	$ 47,907	$ 17,379	$ 92,601	$ 47,949