Stockholders' Equity (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stockholders' Equity [Line Items]
Preferred equity shares capital	$ 240,049,000	$ 11,743,000	$ 82,784,000
Net proceeds from the exercise of option awards	169,000	11,000	327,000
Continuous Offering Program [Member]
Stockholders' Equity [Line Items]
Proceeds from issuance of common stock	231,700,000	10,400,000	81,400,000
Additional shares issued	17,800,000	811,000	6,000,000
Continuous Offering Program Subsequent To Year-End February 23, 2012 [Member]
Stockholders' Equity [Line Items]
Proceeds from issuance of common stock	25,000,000
Additional shares issued	1,900,000
Directors And Employees [Member]
Stockholders' Equity [Line Items]
Related compensation costs	3,200,000	1,300,000	1,300,000
Preferred Stock [Member]
Stockholders' Equity [Line Items]
Preferred equity shares capital	5,200,000
Preferred Stock [Member] | Continuous Offering Program Subsequent To Year-End February 23, 2012 [Member]
Stockholders' Equity [Line Items]
Proceeds from issuance of common stock	$ 2,000,000
Additional shares issued	140,000
$1.26 Cumulative Convertible Preferred Stock, Series B [Member]
Stockholders' Equity [Line Items]
Additional shares issued	365,000