Earnings per Share and Unit (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 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	21,134	17,959
Gain on sale of properties	0	1,834
Less: Noncontrolling interests	314	(383)
Income (Loss) from Continuing Operations Attributable to Parent	20,820	20,176
Less: Preferred stock dividends	5,266	13,937
Less: Dividends paid on unvested restricted stock	216	231
Net income attributable to common stockholders	15,338	12,936
Add: Dividends paid on Treasury Method restricted stock	28	14
Net income for common stock unit/holders - diluted	15,366	12,950
Discontinued operations	0	6,942
Weighted average common shares/units outstanding for basic EPS/EPU	90,112,000	89,497,000
Incremental shares to be issued under unvested restricted stock	61,000	30,000
Weighted average common shares/units outstanding for diluted EPS/EPU	90,173,000	89,527,000
Income per common share/unit - basic:
Continuing operations (in dollars per share)	0.17	0.07
Discontinued operations (in dollars per share)	0.00	0.07
Net income attributable to common stockholders (in dollars per share)	0.17	0.14
Income per common share/unit - diluted:
Continuing operations (in dollars per share)	0.17	0.07
Discontinued operations (in dollars per share)	0.00	0.07
Net income attributable to common stockholders (in dollars per share)	0.17	0.14
Partnership Interest [Member]
Earnings Per Share [Abstract]
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	21,134	17,959
Gain on sale of properties	0	1,834
Less: Noncontrolling interests	275	192
Income (Loss) from Continuing Operations Attributable to Parent	20,859	19,601
Less: Dividends paid on unvested restricted stock	216	231
Net income attributable to common stockholders	15,377	12,990
Add: Dividends paid on Treasury Method restricted stock	28	14
Net income for common stock unit/holders - diluted	15,405	13,004
Discontinued operations	0	6,942
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest	0	14
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0	6,928
Less: Preferred unit distributions	5,266	13,308
Weighted average common shares/units outstanding for basic EPS/EPU	90,289,000	89,674,000
Incremental shares to be issued under unvested restricted stock	61,000	30,000
Weighted average common shares/units outstanding for diluted EPS/EPU	90,350,000	89,704,000
Income per common unit - basic
Continuing operations (in dollars per share)	0.17	0.07
Discontinued operations (in dollars per share)	0.00	0.07
Net income attributable to common unit holders (in dollars per share)	0.17	0.14
Income per common unit - diluted
Continuing operations (in dollars per share)	0.17	0.07
Discontinued operations (in dollars per share)	0.00	0.07
Net income attributable to common unit holders (in dollars per share)	0.17	0.14
Segment, Continuing Operations [Member] | Parent Company [Member]
Earnings Per Share [Abstract]
Less: Noncontrolling interests	314	(383)
Net income attributable to common stockholders	15,338	6,008
Net income for common stock unit/holders - diluted	15,366	6,022
Segment, Continuing Operations [Member] | Partnership Interest [Member]
Earnings Per Share [Abstract]
Less: Noncontrolling interests	275	192
Net income attributable to common stockholders	15,377	6,062
Net income for common stock unit/holders - diluted	15,405	6,076