Earnings Per Common Share (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Numerator for basic and diluted earnings per share:
Income from continuing operations attributable to common stockholders	$ 102,885	$ 57,356	$ 171,545	$ 161,445
Discontinued operations		542		7,139
Net income attributable to common stockholders	$ 102,885	$ 57,898	$ 171,545	$ 168,584
Denominator:
Denominator for basic earnings per share - weighted average shares	287,365	156,631	208,470	156,566
Effect of dilutive securities:
Stock options	412	451	458	375
OP units	1,868		630
Restricted stock awards	38	95	57	62
Convertible notes	1,111	764	1,235	450
Denominator for diluted earnings per share - adjusted weighted average shares	290,794	157,941	210,850	157,453
Basic earnings per share:
Income from continuing operations attributable to common stockholders	$ 0.36	$ 0.37	$ 0.82	$ 1.03
Discontinued operations		$ 0.00		$ 0.05
Net income attributable to common stockholders	$ 0.36	$ 0.37	$ 0.82	$ 1.08
Diluted earnings per share:
Income from continuing operations attributable to common stockholders	$ 0.35	$ 0.37	$ 0.81	$ 1.02
Discontinued operations		$ 0.00		$ 0.05
Net income attributable to common stockholders	$ 0.35	$ 0.37	$ 0.81	$ 1.07