Earnings per Share and Unit (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income per common unit - diluted
Weighted Average Limited Partnership Units Outstanding, Basic			177,164	177,164
Parent Company [Member]
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	$ 23,373	$ 12,492	$ 43,525	$ 29,737
Gain on sale of real estate	1,717	(21)	1,717	1,814
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest	316	257	629	(140)
Less: Noncontrolling interests	340	255	654	(128)
Income (Loss) from Continuing Operations Attributable to Parent	24,774	12,214	44,613	31,691
Preferred stock dividends	(5,265)	(5,396)	(10,531)	(19,333)
Less: Dividends paid on unvested restricted stock	185	206	369	411
Net income attributable to common stockholders	31,679	5,491	47,049	18,467
Add: Dividends paid on Treasury Method restricted stock	30	23	52	35
Net income for common stock unit/holders - diluted	31,709	5,514	47,101	18,502
Discontinued operations	12,379	(1,123)	13,361	6,532
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest	24	(2)	25	12
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	12,355	(1,121)	13,336	6,520
Weighted average common shares/units outstanding for basic EPS/EPU	91,422,000	89,489,000	90,742,000	89,462,000
Incremental shares to be issued under unvested restricted stock	64,000	51,000	56,000	37,000
Weighted average common shares/units outstanding for diluted EPS/EPU	91,486,000	89,540,000	90,798,000	89,499,000
Income per common share/unit - basic:
Continuing operations (in dollars per share)	$ 0.21	$ 0.07	$ 0.37	$ 0.14
Discontinued operations (in dollars per share)	$ 0.14	$ (0.01)	$ 0.15	$ 0.07
Net income attributable to common stockholders (in dollars per share)	$ 0.35	$ 0.06	$ 0.52	$ 0.21
Income per common share/unit - diluted:
Continuing operations (in dollars per share)	$ 0.21	$ 0.07	$ 0.37	$ 0.14
Discontinued operations (in dollars per share)	$ 0.14	$ (0.01)	$ 0.15	$ 0.07
Net income attributable to common stockholders (in dollars per share)	$ 0.35	$ 0.06	$ 0.52	$ 0.21
Partnership Interest [Member]
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	23,373	12,492	43,525	29,737
Gain on sale of real estate	1,717	(21)	1,717	1,814
Less: Noncontrolling interests	270	232	545	424
Income (Loss) from Continuing Operations Attributable to Parent	24,844	12,237	44,722	31,139
Less: Dividends paid on unvested restricted stock	185	206	369	411
Net income attributable to common stockholders	31,749	5,514	47,158	18,544
Add: Dividends paid on Treasury Method restricted stock	(30)	(23)	(52)	(35)
Net income for common stock unit/holders - diluted	31,779	5,537	47,210	18,579
Discontinued operations	12,379	(1,123)	13,361	6,532
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest	24	(2)	25	12
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	12,355	(1,121)	13,336	6,520
Preferred unit distributions	5,265	5,396	10,531	18,704
Weighted average common shares/units outstanding for basic EPS/EPU	91,600,000	89,666,000	90,920,000	89,639,000
Incremental shares to be issued under unvested restricted stock	64,000	51,000	56,000	37,000
Weighted average common shares/units outstanding for diluted EPS/EPU	91,664,000	89,717,000	90,976,000	89,676,000
Income per common unit - basic
Continuing operations (in dollars per share)	$ 0.21	$ 0.07	$ 0.37	$ 0.14
Discontinued operations (in dollars per share)	$ 0.14	$ (0.01)	$ 0.15	$ 0.07
Net income attributable to common unit holders (in dollars per share)	$ 0.35	$ 0.06	$ 0.52	$ 0.21
Income per common unit - diluted
Continuing operations (in dollars per share)	$ 0.21	$ 0.07	$ 0.37	$ 0.14
Discontinued operations (in dollars per share)	$ 0.14	$ (0.01)	$ 0.15	$ 0.07
Net income attributable to common unit holders (in dollars per share)	$ 0.35	$ 0.06	$ 0.52	$ 0.21
Continuing Operations [Member] | Parent Company [Member]
Earnings Per Share [Abstract]
Net income attributable to common stockholders	19,324	6,612	33,713	11,947
Net income for common stock unit/holders - diluted	19,354	6,635	33,765	11,982
Continuing Operations [Member] | Partnership Interest [Member]
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest	246	234	520	412
Net income attributable to common stockholders	19,394	6,635	33,822	12,024
Net income for common stock unit/holders - diluted	$ 19,424	$ 6,658	$ 33,874	$ 12,059