Summary of Significant Accounting Policies (Basic and Diluted Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accounting Policies [Abstract]
Net income (loss) attributable to common shareholders	$ 31,416	$ (14,108)	$ (333,601)
Less: Dividends on participating securities	(3,243)	(2,513)	(1,759)
Basic net income (loss) attributable to common shareholders	28,173	(16,621)	(335,360)
Noncontrolling interest in earnings of common unitholders	859	0	0
Diluted net income (loss) attributable to common shareholders	$ 29,032	$ (16,621)	$ (335,360)
Weighted average number of common shares outstanding	252,694	238,920	201,206
Weighted average partnership Units outstanding	6,904	0	0
Other potential dilutive shares	0	0	0
Weighted average number of common shares and potential dilutive securities	259,598	238,920	201,206