Share Capital (Narrative) (Details) (USD $)	0 Months Ended	12 Months Ended
	Feb. 15, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Feb. 01, 2012	Jun. 07, 2011
Schedule of Capitalization, Equity [Line Items]
Common stock, shares authorized		500,000,000	500,000,000
Common stock, par value		$ 0.01	$ 0.01
Common stock, shares issued		82,753,000	59,551,000
Common stock, shares outstanding		82,753,000	59,551,000		111,688,636
Warrants outstanding		$ 0
Warrants outstanding to purchase additional common stock			15,200
Exercise price of warrants			$ 11.00
Warrants expiration date			Apr. 30, 2011
Preferred stock, shares authorized		50,000,000
Preferred stock, par value		$ 0.01
Preferred stock, shares issued		0	0
Preferred stock, shares outstanding		0	0
Public offering date		February 15, 2011
Public offering, shares	23,000,000
Public offering price	$ 12.35
Proceeds from issuance of common shares	275,800,000	275,884,000	489,740,000	107,741,000
Common stock issued under reinvestment plan, shares		1,095	654
Common stock issued under reinvestment plan, value		13,561	8,624
Number of common stock authorized to sell under sales agreement						15,000,000
Number of common stock available to sell under sales agreement		15,000,000
Dividend Reinvestment And Direct Stock Purchase Plan [Member]
Schedule of Capitalization, Equity [Line Items]
Common stock issued under reinvestment plan, shares		9,192	607,902
Common stock issued under reinvestment plan, value		$ 100,000	$ 8,000,000
Shares available for issuance during period shares dividend reinvestment plan		9,400,000