CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Preferred shares, shares authorized	100,000,000	100,000,000
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, shares authorized	150,000,000	150,000,000
Common shares, shares issued	123,521,535	123,444,235
Common shares, shares outstanding	123,521,535	123,444,235
Series B
Preferred shares, dividend yield (as a percent)	8.875%	8.875%
Preferred shares, shares issued	3,450,000	3,450,000
Preferred shares, shares outstanding	3,450,000	3,450,000
Preferred shares, aggregate liquidation preference (in dollars)	$ 86,250	$ 86,250
Series C
Preferred shares, dividend yield (as a percent)	7.00%	7.00%
Preferred shares, shares issued	12,700,000	12,700,000
Preferred shares, shares outstanding	12,700,000	12,700,000
Preferred shares, aggregate liquidation preference (in dollars)	$ 317,500	$ 317,500