Net Income (Loss) Per Common Share Reconciling the Components of Basic and Diluted Net Income (Loss) per Common Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to common shareholders/unitholders	$ 18,683	$ 28,043
Less: Dividends on Participating Securities	(645)	(688)
Basic Net Income (Loss) Attributable To Common Stockholders	18,038	27,355
Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Redeemable	250	392
Diluted Net Income (Loss) Attributable to Common Stockholders	18,288	27,747
Weighted average number of common shares/units outstanding	327,106	314,936
Weighted Average Limited Partnership Units Outstanding	4,387	4,405
Other potential dilutive shares/units	223	230
Weighted average number of common shares/units and potential dilutive securities	331,716	319,571
Subsidiary of Common Parent [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to common shareholders/unitholders	18,933	28,435
Less: Dividends on Participating Securities	(645)	(688)
Basic Net Income (Loss) Attributable To Common Stockholders	$ 18,288	$ 27,747
Weighted average number of common shares/units outstanding	331,493	319,341
Other potential dilutive shares/units	223	230
Weighted average number of common shares/units and potential dilutive securities	331,716	319,571