Earnings per Share and Unit (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Document Period End Date			Jun. 30, 2014
Earnings Per Share [Abstract]
Gain on sale of real estate	$ 1,691	$ 13,127	$ 2,406	$ 13,127
Income per common unit - diluted
Weighted Average Limited Partnership Units Outstanding, Basic	159,338	177,164,000	159,804	177,164
Parent Company [Member]
Earnings Per Share [Abstract]
Income from continuing operations	29,470	21,642	53,811	40,153
Gain on sale of real estate	1,691	1,717	2,406	1,717
Less: income (loss) attributable to noncontrolling interests	413	313	814	622
Income from continuing operations attributable to the Company	30,748	23,046	55,403	41,248
Preferred stock dividends	(5,266)	(5,265)	(10,531)	(10,531)
Less: dividends paid on unvested restricted stock	176	185	353	369
Net income attributable to common stockholders	25,306	31,679	44,519	47,049
Add: dividends paid on Treasury Method restricted stock	(22)	(30)	31	52
Net income for common stock unit/holders - diluted	25,328	31,709	44,550	47,101
Income from discontinued operations	0	14,110	0	16,733
Less: income from discontinued operations attributable to noncontrolling interests	0	27	0	32
Income from discontinued operations attributable to the Company	0	14,083	0	16,701
Weighted average common units outstanding for basic EPU (in shares)	91,975,000	91,422,000	91,958,000	90,742,000
Incremental units to be issued under unvested restricted stock (in shares)	46,000	64,000	33,000	56,000
Weighted average common units outstanding for diluted EPU (in shares)	92,021,000	91,486,000	91,991,000	90,798,000
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.28	$ 0.19	$ 0.48	$ 0.34
Discontinued operations (in dollars per share)	$ 0.00	$ 0.16	$ 0.00	$ 0.18
Net income attributable to common stockholders (in dollars per share)	$ 0.28	$ 0.35	$ 0.48	$ 0.52
Income per common share/unit - diluted:
Continuing operations (in dollars per share)	$ 0.28	$ 0.19	$ 0.48	$ 0.34
Discontinued operations (in dollars per share)	$ 0.00	$ 0.16	$ 0.00	$ 0.18
Net income attributable to common stockholders (in dollars per share)	$ 0.28	$ 0.35	$ 0.48	$ 0.52
Partnership Interest [Member]
Earnings Per Share [Abstract]
Income from continuing operations	29,470	21,642	53,811	40,153
Gain on sale of real estate	1,691	1,717	2,406	1,717
Income from continuing operations attributable to the Company	30,801	23,117	55,498	41,357
Less: dividends paid on unvested restricted stock	176	185	353	369
Net income attributable to common stockholders	25,359	31,749	44,614	47,158
Add: dividends paid on Treasury Method restricted stock	(22)	(30)	(31)	(52)
Net income for common stock unit/holders - diluted	25,381	31,779	44,645	47,210
Income from discontinued operations	0	14,110	0	16,733
Less: income from discontinued operations attributable to noncontrolling interests	0	28	0	32
Income from discontinued operations attributable to the Company	0	14,082	0	16,701
Less: preferred unit distributions	5,266	5,265	10,531	10,531
Weighted average common units outstanding for basic EPU (in shares)	92,134,000	91,600,000	92,118,000	90,920,000
Incremental units to be issued under unvested restricted stock (in shares)	46,000	64,000	33,000	56,000
Weighted average common units outstanding for diluted EPU (in shares)	92,180,000	91,664,000	92,151,000	90,976,000
Income per common unit - basic
Continuing operations (in dollars per share)	$ 0.28	$ 0.19	$ 0.48	$ 0.34
Discontinued operations (in dollars per share)	$ 0.00	$ 0.16	$ 0.00	$ 0.18
Net income attributable to common unit holders (in dollars per share)	$ 0.28	$ 0.35	$ 0.48	$ 0.52
Income per common unit - diluted
Continuing operations (in dollars per share)	$ 0.28	$ 0.19	$ 0.48	$ 0.34
Discontinued operations (in dollars per share)	$ 0.00	$ 0.16	$ 0.00	$ 0.18
Net income attributable to common unit holders (in dollars per share)	$ 0.28	$ 0.35	$ 0.48	$ 0.52
Continuing Operations [Member] | Parent Company [Member]
Earnings Per Share [Abstract]
Net income attributable to common stockholders	25,306	17,596	44,519	30,348
Net income for common stock unit/holders - diluted	25,328	17,626	44,550	30,400
Continuing Operations [Member] | Partnership Interest [Member]
Earnings Per Share [Abstract]
Less: income (loss) attributable to noncontrolling interests	360	242	719	513
Net income attributable to common stockholders	25,359	17,667	44,614	30,457
Net income for common stock unit/holders - diluted	$ 25,381	$ 17,697	$ 44,645	$ 30,509