Equity (Details Textuals) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended		3 Months Ended		6 Months Ended					3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Apr. 30, 2011	Mar. 31, 2011	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Mar. 18, 2011	Dec. 31, 2010	Feb. 28, 2009	Mar. 31, 2011 Minimum [Member]	Jun. 30, 2010 Minimum [Member]	Mar. 31, 2011 Maximum [Member]	Jun. 30, 2011 Maximum [Member]	Jun. 30, 2010 Maximum [Member]	Jun. 30, 2011 Class G Preferred Stock [Member]	Dec. 31, 2010 Class G Preferred Stock [Member]	Apr. 30, 2011 Underwritten Program [Member]	Apr. 30, 2011 Equity Program [Member]
Class of Stock [Line Items]
Dividend per share															0.080
Cumulative redeemable preferred shares, without par value															$ 0	$ 180,000,000
Dividend yield assumptions										3.00%	3.10%	3.20%	4.20%
Volatility assumptions										36.60%				78.30%
Sale of Stock [Line Items]
Common shares, par value			$ 0.10		$ 0.10			$ 0.10									$ 13.71	$ 25.00
Issuance of warrants, weighted average purchase price					Less than $6.00 per share
Equity (Textuals) [Abstract]
Common shares, issued		10,000,000
Proceeds from issuance of common stock	130,200,000	60,000,000			129,939,000	382,755,000
Aggregate number of common shares to be issued as per Forward sale agreement	9,500,000
Cumulative redeemable preferred shares redemption price	$ 25.105556
Redeemable preferred stock dividend per share prorated to redemption date	$ 0.105556
Write-off of original preferred share issuance costs			(6,402,000)		(6,402,000)
Dividend declared per common share			$ 0.04	$ 0.02	$ 0.08	$ 0.04
Increase to paid-in-capital					2,200,000
Number of common shares purchased under issuance of warrants									10.0
Issuance of warrants, exercise price per share		$ 6.00							$ 6.00
Derivative instruments fair value							$ 74,300,000