CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Preferred shares, par value (in dollars per share)
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	200,000,000	200,000,000
Common shares, shares issued	139,831,549	123,637,424
Common shares, shares outstanding	139,831,549	123,637,424
Series C
Preferred shares, dividend yield (as a percent)	7.00%	7.00%
Preferred shares, shares issued	0	6,700,000
Preferred shares, shares outstanding	0	6,700,000
Preferred shares, aggregate liquidation preference (in dollars)	$ 0	$ 167,500
Series D
Preferred shares, dividend yield (as a percent)	7.125%	7.125%
Preferred shares, shares issued	11,600,000	11,600,000
Preferred shares, shares outstanding	11,600,000	11,600,000
Preferred shares, aggregate liquidation preference (in dollars)	$ 290,000	$ 290,000