SHAREHOLDER'S EQUITY (Details) (USD $)	3 Months Ended		0 Months Ended	3 Months Ended			0 Months Ended	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Jan. 17, 2013 Series A LLC Preferred Shares	Mar. 31, 2013 Series A LLC Preferred Shares	Mar. 31, 2013 Restricted common shares	Mar. 31, 2012 Restricted common shares	Feb. 14, 2013 Restricted common shares Manager	Mar. 31, 2013 Restricted common shares Manager	Mar. 31, 2012 Restricted common shares Manager	Mar. 31, 2013 Restricted common shares Directors	Mar. 31, 2012 Restricted common shares Directors	Mar. 31, 2013 Common share options	Mar. 31, 2012 Common share options
Stock-based compensation
Preferred shares, shares issued	14,950,000	0	14,950,000
Preferred shares, dividend rate (as a percent)			7.375%	7.375%
Gross proceeds from issue of preferred shares (in dollars)			$ 373,800,000
Net proceeds from issuance of preferred stock (in dollars)	361,622,000		362,000,000
Exercise price of share options granted, minimum (as a percent)												100.00%
Termination period from date of grant												10 years
Authorized shares available to satisfy awards as of the balance sheet date												8,839,625
Vesting period							3 years
Restricted common share transactions
Unvested shares at the beginning of the period					531,190			438,937		92,253
Issued (in shares)					292,009		292,009	292,009
Vested (in shares)					(146,312)			(146,312)
Unvested shares at the end of the period					676,887			584,634		92,253
Value of unvested restricted common shares granted (in dollars per share)								$ 11.07	$ 9.21
Unrecognized compensation cost (in dollars)					5,300,000	3,900,000
Number of Options
Outstanding at the beginning of the period (in shares)												1,932,279
Outstanding at the end of the period (in shares)												1,932,279
Exercisable at the end of the period (in shares)												1,932,279	1,932,279
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)												$ 20.00
Outstanding at the end of the period (in dollars per share)												$ 20.00
Share-based compensation expense (in dollars)					$ 980,000	$ 614,000		$ 719,000	$ 383,000	$ 261,000	$ 231,000