CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Preferred shares, par value (in dollars per share)	$ 0	$ 0
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	149,920,449	149,606,024
Common shares, shares outstanding	149,920,449	149,606,024
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