CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
CONSOLIDATED BALANCE SHEETS
Preferred shares, par value (in dollars per share)	$ 0	$ 0
Preferred shares, shares authorized	100,000,000	100,000,000
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
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	149,950,760	149,920,449
Common shares, shares outstanding	149,950,760	149,920,449